Groove selections change the meter in Capcom vs. SNK 2, Capcom's 2001 crossover of both companies' fighters. Ryu and Terry Bogard can share a team, and the GameCube edition is the EO revision of that arcade game.
Grooves decide whether a bar is a cancel, a parry, or a custom stock, which is the system the title is built on. The ratio of strong and weak fighters from the earlier crossover is part of the team building.
EO is the revision on the cube. The arcade grooves are the fight, and this edition is that revision rather than the first cabinet people had to leave downtown.