in Japan, a young person who is very interested in and knows a lot about computers, computer games, anime (= animated films), etc., but may find it difficult to talk to people in real life

Hordes of otaku file in, dressed as their favourite video game characters. 成群结队的电脑游戏迷打扮成自己最喜欢的游戏角色，鱼贯而入。