Damaten
Damaten is a strategy used for closed tenpai hands. This strategy may also be referred to as a "hidden tenpai". Riichi is an optional play, rather than a mandatory one. For damaten, a player opts not use utilize riichi. Usually, players tenpai hands during damaten already possesses at least one valid yaku.
Meaning
Usage
The major weakness of riichi stems from the inability to change the hand after making the call. In doing so, a player makes oneself vulnerable to the changing conditions of the game. In turn, the player may become susceptible to playing into another player's hand.
Also, adding the yaku of riichi may not actually improve the value of a hand instantly. For example, a haneman hand is worth 6 or 7 han. Well, if a player's hand currently appears to be valued 6 han, it may not be necessary to take the risk of riichi just to upgrade the hand from 6 han to 7.
Finally, a player may not actually want to announce their hand as a tenpai hand. Instead, a damaten hand awaits for other players to unexpectedly play into the hand.