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サイズは売り切れです。
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?
L size; larger than M.
From English 'S' (small) + サイズ (size).