It’s been in the series as an item since Melee, and one of my favorites. It’s from the Metroid games, where Samus can equip it and attack enemies while jumping.
All you have to do is pick one up and the fighter automatically wears it.
Though I always thought it was a little wrong considering Samus is an original fighter and she already has this move.
But it is more powerful than Samus already, so it would make sense to grab it if you were playing as Samus. I always liked this one because it’s not super-powerful but it is very useful and comes in handy quite often.