Definition of Excuse

A reason alleged for doing or not doing a thing. A matter alleged as a reason for relief or exemption from some duty or obligation. That which is offered as a reason for being excused, or a plea offered in extenuation of a fault or irregular deportment. It is that plea or statement made by the accused which arises out of the state of facts constituting and relied on as the cause. See also Defense.

That's the definition of Excuse in Black's Law Dictionary 6th Edition. Courtesy of Cekhukum.com.