Ｓサイズ

noun

S size; small size

Refers to the smallest standard clothing or product size, often used in retail and fashion contexts.

• このＴシャツのＳサイズは売うり切きれです。

  The S size of this T-shirt is sold out.

• ＳサイズとＭサイズ、どちらがよろしいですか。

  Which would you prefer, S size or M size?