Input latency
Also said as Input lag, Button-to-pixel delay
The time between pressing a button and seeing the result on screen. Every stage adds some: the controller, the game's frames, the display.
People cannot name it, but they feel it. Above a tenth of a second, a game starts to feel as if you are suggesting things rather than doing them.
Say it
“Keep button-to-pixel latency under 50 ms. The character starts moving on the same frame as the press, and no animation can delay it.”
Where you’ve seen it
Rhythm games such as Guitar Hero include a calibration screen to measure and offset this delay, because timing the music depends on it.
Not to be confused with network latency
Input latency is on your own machine. Network latency is between machines. Both add up in an online game, but they have different fixes.