凸

A pictograph representing a surface bulging outward at the center.

Simple iconic form: the middle part raised higher than the sides.

Paired with 凹 (“concave”) as an antonym set.

Semantic range:

- convex, bulging, protruding;

- by extension: raised printing, embossing (凸版);

- antonym of 凹 (concave).

凹凸 (요철) — unevenness, concavity and convexity

凸版印刷 (돗판 인쇄) — relief printing, letterpress printing

In Korean Internet slang, 凸 is nicknamed 철구 (철 + 9, from the Windows input sequence) and widely used as a textual middle-finger gesture due to its resemblance to the raised middle finger.

In Japanese slang, 凸 is read でこ (deko) “forehead,” leading to nicknames like おでこちゃん for characters with prominent foreheads. It also appears in pop culture (e.g., the idol group 凸レーション / Dekoration in THE iDOLM@STER).

In online Japanese, 凸る (とつる) is a slang verb meaning “to突撃 (rush, storm in),” often shortened to “den-totsu” (電話凸) = “phone call barrage.” By extension, it now means showing up unexpectedly in online spaces or joining streams without prior notice.