dead thread; inactive thread
Internet slang for a forum or bulletin board thread that has become inactive, with few or no recent posts. Often used on 2channel-style boards.
This thread is already a dead thread, so no one posts in it anymore.
It's hard to revive an inactive thread.
Compound of 過疎 (かそ, 'depopulation') and スレ (abbreviation of スレッド, 'thread'). The term emerged in Japanese internet culture to describe forum threads with very low activity.