The term 'turns in' can have several meanings. In the context of a crossword puzzle, it could refer to the action of redeeming, retiring, submitting, crashing, or hitting the hay. To redeem something is to exchange it for something of value, such as money or goods. To retire something is to take it out of use or circulation. To SUBMIT something is to offer it for consideration or approval. To crash something is to cause it to fail or break down. Finally, to hit the hay is an informal phrase meaning to go to bed.