Telemetry is when companies measure and collect your usage of their product, in theory so they can improve it, know which features are used and which not, where

Telemetry is when companies measure and collect your usage of their product, in theory so they can improve it, know which features are used and which not, where users spend most time, etc. As it is a kind of vague definition and you (almost) never know exactly what information is being transmitted, and given the fact that it is Google (or Microsoft, or Apple, or whatever), people sometimes rather just disable telemetry at all.