Buying proxies means reading specification sheets written in a vocabulary nobody explains, where the same word can mean different things on two vendors’ sites. This is the working glossary: the terms that actually change what you pay or what you get, grouped by the decision they belong to, in plain language.
Proxy types
Residential proxy. An IP address belonging to a real home internet connection, assigned by a consumer ISP to a household. Sites treat it as an ordinary visitor, which is why it works on targets that block servers. Sourced from people who agreed to share their connection, so the supply is finite and the price reflects that. More in what residential proxies are.
Datacenter proxy. An address belonging to a hosting or cloud provider. Fast, cheap, plentiful, and instantly recognisable as a server because the address ranges are publicly registered. Fine for undefended targets, poor for anything that scrutinises traffic. The comparison is in residential versus datacenter.
ISP proxy, also called static residential. A hosted address registered to a consumer ISP: residential-grade trust with datacenter stability and speed, and it does not rotate. Right when you need the same identity to persist rather than to change. See ISP versus residential.
Mobile proxy. An address from a carrier’s mobile network. The hardest type to block because carriers put many real subscribers behind each address, and correspondingly the most expensive and least stable. See mobile versus residential.
Proxy pool. The set of addresses a provider can route you through. The headline number is a weak comparison metric, because what matters is density in the countries you actually use and how many are concurrently available, not a cumulative count.
How traffic is routed
Gateway. A single endpoint you send everything to, which picks an exit address for you based on parameters you supply. The alternative, now largely historical, is a list of individual proxy addresses and ports you manage yourself.
Rotating proxy. Each request exits through a different address. The default for bulk collection, because it spreads volume so no single address draws attention. See how rotation works.
Sticky session. One address held across several requests, identified by a session ID you choose, for a limited lifetime. Necessary for multi-step flows where the site tracks state, such as a search that pages or a login. See sticky versus rotating.
Session ID and TTL. The session ID is the label that ties requests to the same exit address; the TTL is how long that mapping survives before the address rotates. Both are usually expressed inside the proxy username rather than as separate settings.
Concurrency. How many requests you have in flight simultaneously. Distinct from rate, which is how often you start them, and some providers meter it separately. See unlimited concurrent connections.
Targeting
Geo-targeting. Choosing which country the exit address sits in, so you see what a visitor there sees. The foundation of any collection where results vary by market.
City-level targeting. Narrowing to a specific city, which matters for local search, store availability, and regional pricing, and is unnecessary for most other work. See when city-level targeting matters.
ASN targeting. Choosing the network operator the address belongs to, useful when a target behaves differently by carrier. See ASN targeting.
Strict matching. An option that fails the request rather than falling back to a broader area when no address matches your filter exactly. Useful when a wrong location would silently corrupt data.
Pricing and billing
Per-GB pricing. You pay for data transferred, not for addresses or ports. This is the standard model for rotating residential and it makes bandwidth, not IP count, the number to forecast. See estimating monthly bandwidth.
Bandwidth allocation. The GB included in your plan for a billing cycle. Typically does not roll over.
Overage, sometimes called extra traffic. What happens when you exceed the allocation: either requests stop, or usage continues at a per-GB rate charged against a balance, depending on how the account is configured.
Per-port or per-IP pricing. The older model where you bought a fixed number of ports or addresses. Largely superseded for rotating residential, and worth understanding mainly so you recognise it in a quote. See why the per-port era is over.
Quality and trust
IP reputation. The accumulated judgement sites and intelligence services hold about an address, based on what has been done from it before. A genuinely residential address with poor reputation performs worse than a clean one, which is why reputation matters as much as type. See what IP reputation is.
Fingerprinting. Identifying a client from the characteristics of its requests rather than its address: TLS handshake, HTTP/2 settings, header set and order, and in browsers the rendering and device details. A clean IP with a mismatched fingerprint still gets caught. See TLS and HTTP/2 fingerprinting.
Soft block. A refusal disguised as a success: a challenge page, an empty result, a truncated listing, or a generic page returned with a 200 status. The most expensive failure mode, because naive monitoring counts it as working. See detecting blocked or fake content.
Validated success rate. The share of requests that returned the data you wanted, as opposed to the share that returned any response at all. The only success metric worth reporting. See proxy KPIs.
Ethical sourcing. Whether the people whose connections make up the pool knowingly agreed and can opt out. A supply-chain question with practical consequences, since undisclosed sourcing correlates with pools that get flagged.
Operations
Rate limiting. A target’s cap on how many requests it accepts in a period, usually per IP. Your pacing has to respect it, and a pool changes where the limit binds rather than removing it. See rate limiting and throttling.
Backoff. Waiting progressively longer between retries after a failure, ideally with randomisation so parallel workers do not retry in synchronised waves. See retry and backoff.
Failover. Moving work to a different route when one degrades, so a job continues rather than stalling. See failover in multi-region pipelines.
407. The status code a proxy returns when it rejects your credentials. Usually wrong credentials or a malformed targeting flag, and never worth retrying. See fixing 407 errors.
Uptime SLA. A commitment about the provider’s own availability. It says nothing about whether your targets accept your traffic, which is a separate axis you monitor yourself. See SLAs and uptime guarantees.
Terms worth being sceptical about
Three phrases carry less information than they appear to.
“Unlimited.” Always ask unlimited in which dimension. Unlimited concurrency is meaningful; unlimited bandwidth on a residential product usually is not, and where it appears there is generally another limit doing the work.
“99.9% success rate.” No provider controls whether third-party sites accept your traffic, so a success-rate claim on arbitrary targets is not a promise anyone can keep. Test on your own targets instead, per testing speed, success rate and location accuracy.
Pool size in the tens of millions. Unverifiable, and not what determines your results. Density where you collect is, and that shows up in your own measurements rather than on a marketing page. If you want to check whether a pool is what it claims, see spotting datacenter IPs sold as residential.
The bottom line
Most of the vocabulary reduces to four decisions: which type of address you need, how it should rotate, where it should be, and how you are billed for it. Everything else is either a quality question, which your own testing answers better than any specification sheet, or an operational one you will meet after you buy. When a term is doing persuasive work rather than describing something measurable, treat it as marketing and go and measure the thing yourself.
When you are ready to compare that against a real product, residential proxies cover the rotating, sticky, country and city cases described above through one gateway, with per-GB pricing so the number you forecast is the number you pay. The plan-level decisions are in choosing the right residential proxy plan.