Definition of overpair
The word overpair could be translated as "overpair". A overpair is a top pair in the table. If you have a pair of 9s on 4-4-5, you have a overpair at the flop. If the turn is a jack, we have a overpair on the flop, but not on the board (which includes the turn). To have a overpair, we would need to have a pair of queens and better. Most of the time, a overpair will be the best hand on the flop. To use our example above, 99 will have about 65% equity against a classic cutoff (let's assume we're on the big blind).
Overpair on the flops wet vs overpair on the flops dry
Let's take a hand like KK preflop. If we are against an 18% range on a dry flop like 8-8-9, we will have 80% equity against our opponent's full range. But if we change a single card on the flop to make it more dynamic (wet ) and an 8 becomes a T that makes a flush draw, KK's equity drops from 80% to 60%, which is considerable. In summary, overpairs must be played slowly on the dry boards and quickly on the dynamic boards (wet boards).