An XO-Suit is a form of powered armor used by Humans. They are typically used to protect the wearer from hostile environments such as the vacuum of space, deep underwater, or the middle of a battle between warring factions of giant robots. The XO-Suit has the ability to transform into several different modes of transportation including the head of a Zapbot that the human is using for a larger body.
Behind the Scenes
Of course, as a kid, I have no idea how this was spelled and from the Transformers Movie, I thought they said 'XO' instead of 'Exo.' As I wrote the stories the XO-Suit is very similar to what you have seen in the modern-day IronMan movies in that it had multiple uses and could transform into its own vehicle mode as needed as well as the head of the Zapbot. The Headmaster setup is more similar to the Japanese Version of Transformers in that, there is no binary bonded robot, and the suits are just an interface for a larger Zapbot body for the humans to use.