Proxy providers, anti-bot vendors and scraping tools share a vocabulary that is rarely explained in one place. This glossary defines the terms you will actually meet — in dashboards, pricing pages, error messages and forums — in a few sentences each. Entries are alphabetical; where a concept deserves a full article, the entry links to it.
A–C
Anonymous proxy
An HTTP proxy that hides your IP but still adds headers (such as Via) revealing that a proxy is in use. Sits between transparent and elite. For privacy or automation you want elite; see how to test anonymity level.
Anti-bot / anti-fraud system
Software on the website's side that scores each request or session for automation likelihood using IP reputation, browser fingerprint, behaviour and challenge results, and responds with rate limits, CAPTCHAs or blocks. Cloudflare Bot Management, DataDome, PerimeterX (HUMAN) and Akamai Bot Manager are the names you will see most.
Antidetect browser
A browser that runs isolated profiles, each with its own consistent fingerprint, storage and bound proxy, so multiple accounts on one machine appear to be unrelated devices. Explained in What is an antidetect browser.
ASN (Autonomous System Number)
The number identifying the organisation that routes a block of IP addresses — an ISP, a hosting company, a mobile carrier. Anti-bot systems look up an IP's ASN to decide whether it belongs to a household, a datacenter or a phone network. It is the technical basis of the datacenter/residential/mobile distinction.
Backconnect proxy
A single gateway address that forwards each connection to a different exit IP from the provider's pool. You configure one host and port; rotation and geo-targeting are controlled through parameters in the username. Almost all residential and mobile proxies are sold this way; see how backconnect gateways work.
Bandwidth (traffic) billing
Pricing per gigabyte transferred through the proxy, typical for residential and some mobile plans. Contrast with per-IP or per-port billing. Bandwidth-heavy tasks (pages with many images, video) become expensive quickly on per-GB plans.
Blocklist / blacklist
A published list of IP addresses associated with abuse (spam, attacks, prior bot activity). Spamhaus and SORBS are examples. Sites and mail servers consult them; an IP on a blocklist should not be used for email, forms or account creation.
CAPTCHA
A challenge intended to be easy for humans and hard for scripts. Modern versions (reCAPTCHA v3, Turnstile) often run invisibly and score behaviour rather than showing puzzles. Frequent CAPTCHAs are a signal that the target distrusts your IP or fingerprint.
CGNAT (carrier-grade NAT)
The technique mobile carriers (and some ISPs) use to share one public IPv4 address among many subscribers. It is why mobile proxy IPs are so hard to ban: blocking one address blocks hundreds of real users. Explained in the proxy types comparison.
Concurrency (threads)
The number of simultaneous connections a proxy plan allows. Scraping throughput is bounded by concurrency × per-request speed; plans often cap it, and exceeding it yields errors rather than slower service.
CONNECT method
The HTTP request a client sends to an HTTP proxy to open a raw tunnel to a destination, used for HTTPS. The proxy relays encrypted bytes without seeing inside. This is what makes an “HTTPS proxy” work.
D–H
Datacenter proxy
A proxy whose IP is registered to a hosting or cloud company. Fast, cheap, plentiful, and the easiest type for websites to recognise as non-residential. Details and trade-offs in Residential vs datacenter vs mobile.
Dedicated (private) proxy
An IP used by only one customer. Its reputation is entirely yours to build or ruin. Contrast with shared.
DNS leak
When domain-name lookups go to your normal resolver instead of through the proxy, so your ISP still learns which sites you visit even though the sites see the proxy's IP. Fixed by remote DNS resolution (SOCKS5 h mode) or by using an HTTPS proxy. See testing for leaks.
Elite (high-anonymity) proxy
An HTTP proxy that adds no identifying headers, so the destination sees a request that appears to originate from the proxy itself. The standard for commercial privacy and automation proxies. See our elite proxy ranking.
Exit IP (exit node)
The IP address the destination website actually sees — the last hop before the target. With a backconnect gateway the exit changes while your configured host does not.
Fingerprint (browser fingerprint)
The combination of properties a browser reveals — canvas and WebGL hashes, fonts, screen, User-Agent, time zone, audio — that together identify a device even without cookies. Not changed by a proxy; changed by an antidetect browser.
Forward proxy
A proxy that acts on behalf of the client, hiding it from servers. Everything sold as “proxies” for scraping or accounts is a forward proxy. Contrast reverse proxy. Basics in What is a proxy server.
Gateway
See backconnect proxy. The provider's entry point that assigns exit IPs.
Geo-targeting
Selecting the country, region or city of the exit IP, usually via parameters in the username. Precision varies: country is universal, city is common for residential, and mobile IPs are often geolocated to the carrier's head office rather than the phone.
HTTP proxy
A proxy that understands HTTP requests. It can read, cache or modify plain HTTP and tunnels HTTPS via CONNECT. Configured in browsers and most tools. Compare SOCKS5; the full comparison is SOCKS5 vs HTTP proxies.
I–P
IP whitelist (IP authorisation)
Authenticating to a proxy by registering your own public IP with the provider instead of using a username and password. Convenient on servers with static IPs; impractical on connections whose IP changes.
ISP proxy (static residential)
A residential-registered IP hosted on the provider's own servers, giving residential reputation with datacenter speed and a static address. Often the best choice for one long-lived account per IP.
Latency
Round-trip time added by the proxy hop, in milliseconds. Datacenter: tens of ms; residential and mobile: 50–300 ms. Governs how fast sequential requests can go; measured with a small request and compared to a direct connection.
Mobile proxy
A proxy whose exit IP belongs to a cellular carrier, delivered through real SIM cards. Highest trust because of CGNAT, highest price, and rotation by modem reconnect. See mobile proxies in practice.
PAC file (Proxy Auto-Config)
A small JavaScript file the OS or browser loads that returns, per URL, which proxy to use or DIRECT. Lets you proxy some sites and not others. Configured in the “automatic” section of Windows and macOS proxy settings; see the setup guide.
Pool
The set of exit IPs a provider can assign you. Size is advertised heavily; what matters more is freshness — how recently other customers used those IPs on your target.
Port
The number after the colon in a proxy address (host:port). Different ports on the same host may map to different protocols or, with mobile providers, to different physical modems (“per-port billing”).
Proxy chain
Routing traffic through two or more proxies (or a VPN and a proxy) in sequence. Adds hops and latency; used to hide proxy use from a local network or to combine properties. Discussed in Proxy vs VPN vs Tor.
R–S
Rate limit
A per-IP (sometimes per-account) cap on requests in a time window, enforced by the target with HTTP 429 or slowdowns. The main reason rotation exists.
Residential proxy
A proxy whose exit IP was assigned by a consumer ISP to a household. Looks like an ordinary visitor; usually billed per GB and rotating. See Residential vs datacenter vs mobile.
Reverse proxy
A proxy that acts on behalf of the server: load balancing, TLS termination, caching, attack filtering. Cloudflare and Nginx in front of a site are reverse proxies. Not what proxy providers sell.
Rotation
Changing the exit IP per request, on a timer, or on demand, to spread activity across addresses. Explained fully in What is IP rotation.
Session (sticky session)
A mode where the gateway holds the same exit IP for a named session for a set time, so cookies and logins survive across requests. Selected by passing a session ID in the username. The counterpart of per-request rotation.
Shared proxy
An IP used by several customers simultaneously. Cheaper than dedicated; you inherit whatever reputation the others create. Fine for tolerant targets, risky for accounts.
SOCKS5
A proxy protocol one level below HTTP that forwards any TCP (and UDP) traffic without understanding it. Works for any application, supports remote DNS resolution and authentication. Compared with HTTP in SOCKS5 vs HTTP proxies.
Static IP
An exit IP that stays the same for as long as you rent it. Wanted for accounts and whitelisting; the opposite of rotating. Offered as datacenter, ISP, or dedicated mobile ports.
Subnet
A contiguous block of IP addresses, e.g. 203.0.113.0/24 (256 addresses). Bans and reputation often apply to whole subnets, which is why datacenter IPs from one block can all be flagged together and why “IPs from many subnets” is a selling point.
T–W
Throughput (bandwidth)
How much data per second the proxy can move — the number that matters for bulk downloads and many parallel connections, as opposed to latency. Highest on datacenter, bounded by the host connection on residential and by cell coverage on mobile.
Transparent proxy
An HTTP proxy that forwards your real IP in an X-Forwarded-For header. Provides no privacy; used by corporate and ISP caches. If a “privacy” proxy turns out to be transparent, stop using it.
User-Agent
The header in which a browser or tool announces what it is. Should be consistent with the proxy type and profile (a desktop UA on a mobile carrier IP is a mismatch) and, in automation, should look like a real current browser.
VPN
An encrypted tunnel that routes all of a device's traffic through one server. Compared with proxies and Tor in Proxy vs VPN vs Tor.
WebRTC leak
Browsers can expose your real local and public IP to a web page through WebRTC connection negotiation, bypassing the proxy. Disable WebRTC or use a browser that spoofs it to the proxy IP. Testing steps in How to test a proxy.
Whitelist
See IP whitelist. Also used for the list of destinations that bypass a proxy in OS settings (“bypass list”).
Frequently asked questions
What is the difference between a proxy pool and a subnet?
A pool is the whole set of IPs a provider can assign you, drawn from many networks. A subnet is one contiguous block of addresses. A good pool spans many subnets, so a ban on one block does not empty it.
What does “backconnect” mean on a pricing page?
That you get one gateway address and the provider rotates exit IPs behind it, rather than a fixed list of IPs. It is the normal delivery method for residential and mobile proxies.
Is a sticky session the same as a static IP?
Not quite. A sticky session holds one exit IP for minutes to hours and then may change; a static IP is yours for the rental period. Sticky is a rotation mode; static is a product type.
What is an ASN and why do proxy providers mention it?
The number identifying which organisation routes an IP. Providers mention it because anti-bot systems classify IPs by ASN into hosting, ISP or mobile — so “real ISP ASNs” is a claim about how residential the IPs will look.
Which terms should a beginner learn first?
Forward proxy, the three IP types (datacenter / residential / mobile), HTTP vs SOCKS5, rotation vs sticky, and the two leaks (DNS, WebRTC). Those six cover almost every decision when buying and configuring a first proxy.