“Move balance” is all about the spread of capabilities between different moves (e.g., normal, special, and command moves). This does not have much to do with game balance, necessarily, unless of course some character’s move balance is too good in comparison to everyone else’s.
When it comes to an individual character’s move balance, one should seek out the offensive and defensive capabilities in order to best take advantage of them.
It’s generally good if anti-air moves, projectiles, and rushing moves (or any moves that can be used for zoning) complete some sort of set. This is particularly true of the standard “shoto-clones”: shoto-clones have equivalents to (or actually have) Shōryūken, Hadōken, and Tatsumaki Senpūkyaku in these respective rôles. If these allow for a decent opportunity to attempt offense or defense (or perhaps some sort of fireball trap tactic), then one can say that a character has good move balance (as long as game balance issues do not need to be addressed).
Inversely, if the range, speed, or strength (etc.) are particularly lacking in some (or many) areas, one can say that a character has bad move balance.
When it comes to a game as a whole, if particular characters’ moves are too strong or too weak, the move balance is bad. If neither is the case, the move balance is good.