A "skeleton costume" is an outfit or getup that makes someone look like a skeleton, which is the bony framework of the human body. It is usually worn during Halloween or costume parties to portray a spooky or creepy appearance. Full definition
Oh yeah, and needless to say: It's also the best skeleton costume in the world! (geekwrapped.com)
Here's a comfy skeleton costume that any baby wear. (easybabylife.com)
People in Mexico (and around the world) observe the holiday with offerings of food, flowers, and music for the dead, as well as skeleton costumes and candy for the living. (businessinsider.com)