gym clothes; gym uniform; PE kit
Refers to the clothes worn for physical education classes or sports activities at school. Often a specific uniform set.
See also: 体操服
We have PE tomorrow, so don't forget your gym clothes.
体操着に着替えてグラウンドに集合してください。
Please change into your gym uniform and gather on the field.
Compound of 体操 (gymnastics, physical exercise) and 着 (clothing, wear).