Mostly in 2D fighting games, and in most of them, command moves (aka command normals; in Japanese, they are tokushu waza, which means ‘special move’... but don’t confuse that with the English special move for a moment!) are moves that you can perform by having the directional input a particular way and pressing a button.
Unlike a special move, there is no need to do any stick twirling. In some cases, command moves are performed by simultaneous presses, making the stick input unnecessary.
Command moves tend to be like slightly special normals; e.g., the startup could be slower, in return for an overhead hitbox, or the moves could be more conducive to tactics during general conduct.
These moves usually have names, but there are plenty of games where they don’t.