树洞

樹洞
shùdòng
  1. tree hollow
  2. (slang) anonymous platform for sharing secrets
  3. (slang) confidant

CEDICT

slang

Entry Composition

1 树 shù
  1. tree
  2. to cultivate
  3. to set up

classifier: 棵
2 洞 dòng
  1. cave
  2. hole
  3. zero (unambiguous spoken form when spelling out numbers)

classifier: 個