Could someone explain "donkbet"

Been lurking these forums for a while and seen this term Donkbet used frequently. From what ive seen, it is a lead out bet in one of two situations:

1) A lead out from the SB/BB into PF raiser or
2) a lead bet into a flop or turn raise.

Correct? What I am trying to figure out is what the donk bet indicates? It seems like people use this on the when raised on the flop of a draw heavy board, they are leading out in order to avoid a free card. In the other case, the BB leads out because they have an average hand and are trying to figure out where they stand. Are my assumptions correct? What type of hands does the usual donkbetter bet with and whats the goal of this bet. How should you interpret and react to these bets. I know this is a vague question and each situation is usually player read and board dependent, but am trying to figure what the donkbet means and what are the mistakes made by leading in certain situations.