What is what: the split by time control
FIDE classifies chess by how much time a player has, counting the increment as well. A rough but reliable calculation: take the base time and add 60 times the increment per move (as if the game lasted 60 moves).
- Classical (standard): around 60 minutes or more per player.
- Rapid: more than 10 but less than 60 minutes.
- Blitz: 10 minutes or less.
Example: 3+2 means 180 + 60x2 = 300 seconds, so 5 minutes, which is blitz. And 10+5 gives 600 + 300 = 900 seconds, that is 15 minutes, so rapid.
Typical time controls
- Blitz: 3+2, 5+0, 5+3.
- Rapid: 10+5, 15+10, 25+10.
The increment (for example "+2") gives you a little time back after every move, so you do not lose a winning position simply because you have no time left to move your hand.
Illegal moves
This is where the difference from classical chess is biggest. When an arbiter is watching the game: the first illegal move gives the opponent extra time (usually two minutes), and a second illegal move by the same player means a loss. When there is no arbiter at every board (common in blitz), the opponent may stop the clock and claim a win because of an illegal move, but only if they have not yet made their own next move. The moment you reply, the lapse is "forgiven".
Time and the falling flag
If your flag falls, you have lost, exactly as in classical chess, only here it happens much more often. The one exception: if your opponent does not have enough material to mate you at all (say, only a bare king is left), the game is a draw rather than a win for them. In blitz without an arbiter you claim a win on time by stopping the clock and calling the organiser.
Why they are rated separately
FIDE keeps three separate rating lists: standard, rapid and blitz. The reason is simple: a player's strength is not the same at every time control. One player shines in classical chess and throws away an advantage in blitz, and the other way round. Separate ratings therefore describe more faithfully how strong you really are at that particular speed, and results at one time control do not affect the list for another.