Glossary
Load Testing Glossary
Load testing has a vocabulary problem. The same word means different things in different tools, and a result is easy to misread when “users” and “response time” are not the numbers you assumed they were.
These are the 20 terms that show up most often in test plans and results, each on its own page with a definition you can quote and the mistakes that definition prevents.
Load Model & Traffic Shape
Concurrent Users
Concurrent users are the users active in a system at the same moment — in a load test, the virtual users holding an open session or an in-flight request.
Load Profile
A load profile is the shape of load over time in a test — how many virtual users are active at each moment, from ramp-up through steady state to ramp-down.
Ramp-Up
Ramp-up is the period over which a test climbs from zero to its target load, adding virtual users gradually instead of starting all of them at once.
Scenario
A scenario is one complete user journey in a load test — an ordered sequence of steps that a virtual user executes from beginning to end.
Think Time
Think time is the pause a virtual user takes between steps to imitate a real person reading, typing, or deciding before making the next request.
Thread Group
A thread group is JMeter’s unit of load: a named pool of threads that each run the same request sequence, with its own user count, ramp-up, and loop count.
Virtual Users (VUs)
A virtual user is a simulated client that runs a test scenario end to end, independently and in parallel with every other virtual user in a test.
Test Types
Breakpoint Test
A breakpoint test ramps load steadily upward until the system violates its targets or fails, in order to find the exact load at which capacity runs out.
Soak Test
A soak test holds a moderate, realistic load for hours or days to surface problems that only appear over time, such as memory leaks and pool exhaustion.
Spike Test
A spike test applies a sudden, extreme jump in load and then removes it, to see whether a system absorbs the surge, sheds it cleanly, or falls over.
Stress Test
A stress test pushes a system beyond its expected peak load to find where it degrades, what breaks first, and whether it recovers once the load drops.
Metrics & Measurement
Error Rate
Error rate is the share of requests in a test that failed — connection errors, timeouts, unexpected status codes, or responses that failed an assertion.
Latency
Latency is the delay before a transfer begins — the time to get a request to the server and the first byte of the answer back, excluding transfer time.
P95 / P99 Percentiles
A P95 of 800 ms means 95% of requests finished within 800 ms. P99 says the same at 99% — both describe the slow tail that an average conceals.
Requests Per Second (RPS)
Requests per second is the number of HTTP requests a system handles each second — the most common concrete unit for expressing load test throughput.
Response Time
Response time is the total elapsed time from sending a request to receiving the complete response — everything the client waits for, network included.
Throughput
Throughput is the rate of work a system completes over time — usually requests, transactions, or bytes per second, measured at the completing end.
Capacity & Correctness
Assertion
An assertion is a check applied to a response during a load test — on status, body, or headers — that decides whether a request genuinely succeeded.
Connection Pool
A connection pool is a fixed set of reusable open connections to a database or upstream service, shared between an application’s concurrent requests.
Saturation Point
The saturation point is the load at which throughput stops rising even as more users arrive — the moment a resource runs out and queueing takes over.
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