also: オタげい
noun
otagei; wotagei; fan dance and chants at idol concerts
A style of synchronized dancing, chanting, and light-stick movements performed by fans (often otaku) at concerts, especially idol group concerts. The term is widely recognized in Japanese pop culture.
アイドルのコンサートで、ファンがヲタ芸を披露した。
At the idol concert, fans performed otagei.
彼はヲタ芸の振り付けを完璧に覚えている。
He has perfectly memorized the otagei choreography.
Compound of ヲタ (a variant spelling of オタク, 'otaku') and 芸 (げい, 'performance, art'). The term emerged in the late 1990s or early 2000s within Japanese idol fan culture to describe the energetic, choreographed cheering routines.