Day Order

Any order to buy or sell a security that automatically expires if not executed on the day the order is placed.

Investopedia Says:
A day order will not be executed if the limit or stop order prices were not met during the day. A way to increase the life of an order is to order securities on a 'good 'till cancelled' basis, where, as the name implies, the trade will not expire until it is cancelled or until it reaches a maximum time limit set by the brokerage.

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Taking control of your portfolio means knowing when to use particular orders and if they pose added costs. The Basics Of Order Entry

Order to buy or sell securities that expires unless executed or canceled the day it is placed. All orders are day orders unless otherwise specified. The chief exception is a Good-Till-Canceled Order (GTC), though even it can be executed the same day if the price is right.