Telemetry
Also said as Analytics, Game analytics, Instrumentation
Data the game records and sends back about what players do: where they quit, how long a level takes, which weapons they use. It should be disclosed and it should not identify people needlessly.
It shows what happens across thousands of players, which no playtest can. It tells you where a problem is, but not why it is happening.
Say it
“Log every level start, death and quit with a timestamp and the position. I want a funnel from the tutorial to the credits, and I want to know the step where we lose the most people.”
Where you’ve seen it
Microsoft's user researchers built a system called TRUE, used on games including Halo 2, that logged events together with video clips of the moment, so a spike in the numbers could be watched as well as counted.
Not to be confused with playtest
A playtest gives you the why from a handful of people. Telemetry gives you the what from all of them. You usually need both.