A dead cat bounce is a recovery in the price of a security (usually a share) that does not indicate any sustained recovery or a significant re-rating. It is a recovery from a very low level to a higher level that is still low by historical standards. The bounce looks significant only because it is from such low levels.
Dead cat bounce is a fairly derogatory term and its use implies a negative opinion of the fundamental valuation of a share and the prospects for a sustained recovery.