What does “bad beat” mean?

A common part of poker terminology, bad beat is used for a very strong hand, which lost in the round. This sometimes happens if a player with a consistently strong hand bets and his initially weaker opponent calls and “hits” at the end a very improbable card combination by luck. Despite that there isn’t a defined hand rank, after which all losses are considered bad beats, the poker rooms offering special bad beat bonuses require most often that the losing hand is at least 4 Kind