In the Hyperdimension Neptunia series, combo is a diverse term referring to a sequence of attacks. Usually, four attacks can be designated in one sequence. When a four-action chain combo is utilized by a character, the player may gain a chance for the character to perform special actions after the end of the sequence.
Combos are setup by setting combo skills to specific buttons (Triangle, Circle, X, and Square). When in battle the player can preform a combo by pressing the buttons in any desired order which will in turn activate the skills selected. The nature of combos and their skills may vary between games, but the general concept remains unchanged.