This is a 'Thermal Set" which means it's made from a special heat-holding fabric. It has a variety of purposes, such as underclothes for snow fun, sleep wear, house wear when it's cold out etc. Usually it isn't worn outside, but the pattern here isn't overly loud / it doesn't 'look like' typical pajama stuff. The top has classic running Sonic with an outline/ shadowed effect in three colors, while the pants are black with a red & blue classic logo.