Vocabulary

Reliability and performance tests

Term	Description
VU	Stands for virtual user — simulated user running test scripts concurrently to emulate real-world traffic.
Latency	Time between sending a request and receiving the first byte of the response. Good latency is below 300 ms.
Throughput	Number of requests successfully handled per unit of time (e.g., requests per second). High throughput is good, low is bad.
Iterations	How many times the test function executes (e.g., one iteration = one simulated user flow like login).
Percentile	Percentile is more useful than average because it shows distribution. E.g., p(90) or p(95) — statistical measure indicating that X% of requests completed in Y ms or less. Example: p(90)<500 means 90% of requests completed in less than 500 ms.
SLO (Service Level Objective)	Target performance/availability goal, e.g.: availability 99.8% uptime, performance 90% of responses within 0.5s.
Threshold	Pass/fail condition in tool k6 tests based on metrics, used to enforce SLOs programmatically. Example: http_req_duration: ['p(95)<500'].
Ramp-up / ramp-down	Gradual increase or decrease in the number of virtual users during a test. Ramp-up avoids sudden spikes. Ramp-down allows graceful termination.
Sleep	Pause between actions in a test to simulate user think-time or pacing. E.g., sleep(1) means 1 second pause.