校服(xiào fú) - school uniform in Mandarin

校服 (xiàofú) is the school uniform. 校 (xiào) means "school" (the same 校 as in 学校, xuéxiào) and 服 (fú) means "clothing", so the compound reads plainly as "school clothing".

Chinese schools take uniform seriously, and pupils usually wear it every day rather than saving it for special occasions, unlike some countries where uniform is only for certain events. 穿校服 (chuān xiàofú), "to wear the school uniform", is the standard phrase, using 穿 (chuān), the verb for putting on or wearing clothes.

A full uniform is a set, so it usually takes the measure word 套 (tào): 一套校服 (yí tào xiàofú), "one (set of) school uniform".