A gig line is a term used to refer to the alignment between a seam on a shirt, a belt buckle and the seam of zippered pants. It is typically a military term used to refer to the alignment of a uniform.
A gig line will typically refer to a man's uniform; however, a female wearing a uniform can have a gig line if her shirt is tucked in. A gig line should be a straight line that follows the seam of the shirt, the end of the belt buckle and the seam of the zippered fly. In addition to military usage, it is a common term used for men's business dress.