It's a measure of your raw typing speed, without factoring in accuracy. It simply counts the total number of keystrokes you make in a minute, regardless of whether those keystrokes are correct or not.
This is different from WPM (Words Per Minute), which measures typing speed with accuracy taken into account.
So, while a higher GKPM might seem impressive, it's not a truly accurate reflection of your typing skill. A more meaningful measure is WPM, which reflects both speed and accuracy.