Blitz chess is fast chess, roughly three to ten minutes per player, and the most played speed online.
FIDE defines blitz as any control where each player has ten minutes or less, counting base time plus 60 times the increment; online the popular flavors are 3+0, 3+2 and 5+0. Blitz has its own separate ratings and its own world championship.
With seconds per move, blitz runs on pattern recognition rather than deep calculation. Simple threats score, well known setups save time, and clock handling is worth real rating points: a slightly worse position with a minute against ten seconds is usually a win.
As training, blitz is a double edged sword. It sharpens openings, tactical alertness and speed, but a pure blitz diet teaches shallow, impulsive habits. Use it to pressure test your repertoire, skim your losses for repeated mistakes, and do your serious thinking at slower speeds.
FIDE counts anything at ten minutes or less per player, with the increment scaled by 60 moves. Online, 3+0, 3+2 and 5+0 are the standard blitz pools; below three minutes you are in bullet territory.
Not in moderation. It builds pattern speed and lets you rehearse openings cheaply, but it cannot teach deep calculation. Pair it with slower games and quick reviews of your blitz losses and it becomes a useful tool.
BetterChess is a practice tool — we make no guarantee you'll reach 1800 or any rating. Definitions are standard chess terminology; every diagram position is checked legal with the same engine the board runs.