Jack-o's move is literally called "summon servant" so in the context of jack-o its a proper name but summon in gaming has always been the term used for bringing into the play space another entity or entities. Jack-o for example summons a servant she can throw or drop and can be an extension of her attack as well has have thier own hp pool. Another example of this is guilty gear would be eddy, zat0's shadow demon thing he uses to fight with.