everyday clothes; casual wear; ordinary clothes
Refers to clothing worn in daily life, as opposed to formal wear or uniforms. Often contrasted with 礼服 (formal wear) or 制服 (uniform).
See also: 普段着
休日は便服で過ごすことが多い。
On holidays I often spend the day in casual clothes.
Please attend the ceremony in formal wear, not everyday clothes.
Compound of 便 (convenience, everyday) and 服 (clothing). The exact historical derivation is uncertain, but the word is used in modern Japanese to mean everyday clothes.