Dead Cat Bounce
A dead cat bounce is a short recovery in a falling market that fails and is followed by further declines.
The phrase says that even a dead cat will bounce if it falls from high enough. After a sharp drop the price can rally quickly as shorts close and bargain hunters buy, tempting people to call the bottom, then roll over to a new low.
Telling a bounce from a true reversal in real time is difficult. Traders watch whether the rally is on rising volume and whether it breaks the previous lower high; see mean reversion for what bounces have tended to do.