These are outfits people wear in order to play a role, in this case for sexual excitement. Many find that costumes, uniforms, are a turn on, by wearing them or by having costumes worn by a partner for excitement in the bedroom.
There loads of costumes that ye can try in the bedroom to spice things up. Talk with your partner about any that you both want to try to make sure they have it. For example, you might want to see your partner in a sexy school uniform, a sexy fireman, but you will need ask before as not to be disappointed. Sometimes it's easier to ask what costumes they have available. They will have something to get you going. Costumes are big part of role-play, as you can be anything you want with a little imagination and confidence.
If the costume comes with props, why not use them in some way? Let your partner tickle you with a feather if they have chosen to dress as a French maid, or ask them to leave on their stockings.Uniforms are all ways a big favourite with us guys.