Command is a diverse term used to classify the various skills in the Hyperdimension Neptunia series. While initially it was used in Hyperdimension Neptunia mk2 to classify combo skills, as of Hyperdimension Neptunia Victory it has been used to classify all skills.
Commands can be used to describe all skill types. From Combo skills to SP skills, literally every move that can be preformed in battle is a command. In mk2 this term was only used to describe combo skills, but in victory and onward it has been used to classify all skills regardless of type.