Latency

Latency is the delay between asking a system to do something and it starting to respond, usually measured in fractions of a second. Low latency feels instant; high latency is the frustrating pause after you tap a button before anything happens.

It is like the gap between flicking a switch and the light coming on: short and you barely notice, long and it feels broken. Latency matters because slow responses quietly drive customers away, and even small delays on a busy website measurably reduce sales and patience.