EX can refer to multiple items or concepts.
The most common usage of EX as a gameplay mechanic introduced in the Street Fighter 3 series. Players can spend a certain amount of super meter when performing a special move to give it bonus damage or properties. To activate an EX move, commonly a player has to press two buttons instead of one when activating the special move, provided he/she has enough super meter. This mechanic has been carried over into Street Fighter 4.
EX may also refer to a series of the Street Fighter Series featuring polygonal graphics and 3D fighting game mechanics.