semiformal attire; semiformal dress
Refers to attire that is less formal than full formal wear but still appropriate for ceremonies, parties, or business occasions. Often contrasted with 正礼装 (formal attire) and 平服 (casual wear).
The dress code for the party is semiformal attire.
Please come in semiformal dress.
平服 is casual wear, much less formal than 略礼装.
Compound of 略 (ryaku, 'abbreviated') and 礼装 (reisō, 'formal attire'), literally 'abbreviated formal wear'.