Measure time betwen request sent by user and received answer - measure in miliseconds - this has the greatest impact in the online services that require an immediate response (telephony, online gaming).
Jitter shows response rate fluctuations, ie ping values. Jitter helps diagnose internet connection stability. The higher the jitter value, the worse the stability of the connection.
It determines how quickly you can download something from the Internet - for example, if you want to play online, download the purchased game.
It determines how fast you can upload something to the Internet - for example, if you want to place photos or videos of vacation on the Internet.