That service can be anything from a[citation needed] memory fetch, to a disk IO, to a complex database query, or loading a full web page.
With basic queueing theory math[1] you can calculate how the average wait time increases as the device providing the service goes from 0-100% busy.
Developers can reduce the response time of a system (for end users or not) using program optimization techniques.
It is also different from deadline which is the length of time during which the task's output would be valid in the context of the specific system.
[3][4] In fast paced competitive games such as Counter-Strike, the response time of a display is crucial for optimal performance.