It probably depends upon the server.
On FICS, for example, normal chess has three different ratings: lightning, blitz and standard, depending on the time controls.
A game is lightning if the expected duration (etime) of the game is less than 3 minutes per player.
A game is blitz if the expected duration (etime) of the game is between 3 and 15 minutes per player.
A game is standard if the expected duration (etime) of the game is greater than 15 minutes per player.
The expected duration is determined by the following formula that takes into account both the Start time and the Increment (Inc) value assuming 40 moves are played:
Expected duration = Start + 2/3 Inc
What does blitz indicates?
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I see players with good rating on internet in standard time control and bad with blitz. And I see the opposite. What exactly does blitz indicates?