OTW is the shortcut for Ones-to-watch. OTW-Cards are one of the most wanted Cards in first months of FIFA, and that for a reason:
The most important transfers of the summer will get an OTW-Card. Beside the fresh design, the cards have a special feature: they are dynamic items.
That means if the player gets in the Team of the Week (or gets another performance -based special card), the card will get an automatic upgrade. So instead of buying one Inform-Card after another, your OTW-Card will improve automatically.
That´s why these cards are pretty expensive on the transfer market, especially at the release of FIFA. With a little knowledge in the world of football, you have the chance to get rich with these OTW-Cards. (Only in FIFA of course)
If one FIFA 21-OTW-Player gets injured, the price of the card will drop. If you are buying them at this point, and hoping the will have a strong comeback, you can make a bunch of coins if this player gets an Inform-Card.