Mattress Land is a store that sells mattresses. Their slogan is "Come on down to Mattress Land!" as heard in the commercial in which the New Directions starred in.
The store casts the New Directions (who are willing to work for free as long as they get on television) in one of their commercials to act and do dialogue, but the kids end up performing Jump instead.
Mattress Land give them payment in the form of a stack of mattresses delivered to their choir room in thanks for all of the hard work they had done, although it is assumed that they never asked for any payment. The stack of mattresses removed their "amateur status," according to Sue. They decide to return them to the store, but Will has already opened and slept on one in his office due to marriage troubles, and Figgins informs him that he can't return a mattress that's been opened and slept on.
The store has not been featured or mention on the show since.