A standing attack is one performed from a state where you are standing (particularly a normal move).
Compared with crouching attacks, the reach is usually longer, and the strike height is usually higher. For these reasons, they are particularly useful in zoning and in checking those jumping in, among other things.
In most 2D games and some 3D games, standing attacks are divided into the following:
Basically, the difference between the two depends on the distance with the opponent. This distance can and often does differ between games, characters, and moves.
With some characters in Street Fighter III, and with Street Fighter Alpha 3 V-ism, the difference can depend on the directional input and instead of the distance.