While dressing this morning I took a moment to ensure the gig line was straight. It tends to be a military term but other para-military groups police boy scouts etc will ensure it is straight also. It is simply the alignment of the seam of the uniform shirt, belt buckle, and uniform trouser fly-seam. In order to be properly dressed, these three should align to form a straight line down the front of a person’s body. A gig in the Air Force was a demerit and to not have your Gig line straight in basic training would result in some form of punishment.