The user has the ability to store whatever they want in another dimension and call it forth at will. In Fairy Tail, it is called requip and its users are: Erza Scarlet, Bisca Mulan (Bisca Connell), Coordinator (Phoenix Priestess).

Other names:

Requip (Fairy Tail

Magic Sachel

Hammerspace

Pocketing

This is one of the most badass users of this power.

https://youtu.be/0PhIKaa-U8w