shù​dòng

anonymous platform

树洞 (樹洞) shù​dòng
anonymous platform noun
a digital space or social media account where people can post secrets or vent anonymously
confidant
a person who listens to one's private thoughts or secrets without judgment
tree hollow
a hole or cavity in the trunk of a tree

Frequency

Written text
1.10 per million

Sources

Definitions
CC-CEDICT
Frequency data
BCC Corpus (BLCU)