Please check the back of your card to distinguish if it is a gift card or a Merchandise Return Card. Terms for use of the card will be stated there.
Merchandise Return Cards are issued when merchandise is returned to the store for a credit.
Gift Cards are purchased for the amount paid in credit.
Some retailers have restrictions for use of Merchandise cards, such as: They can only be used on certain products, or only used in store (not online) for purchases.
Also, some merchants require the person that was issued the card to be the only person that is able to redeem it. That is why some brands are not accepted in the form of Merchandise Return cards on exchange sites.