A cooldown is when a recently played card has been transferred or delegated and can't be played for 24 hours. Cards in a cooldown also can't be listed for rent on the market. For example, if you rent out a card and then cancel the rental, the card will have a cooldown from being used by other players.
PeakMonsters lets you update the price on existing rentals - which is not functionality we currently have in-game. So, you can update the price without taking it off the market and triggering a cooldown on PeakMonsters. If you do it in-game, you have to actually cancel the rental and then relist it, which is a different process.