noun
silent but secretly lovestruck
Manga/anime slang for a character who is outwardly quiet or taciturn but inwardly smitten. From 黙り (damari, silence) + デレデレ (deredere, lovestruck).
あのキャラは典型的なダンデレで、普段は無口だけど実は主人公にベタ惚れだ。
That character is a classic dandere: usually quiet, but actually head over heels for the protagonist.