what do you call the edge that goes along ironed trousers?

Question

When you move a heated iron up and down a pair of trousers it causes the trousers to fold and a resulting line is noticeable on the front of the trousers. what do you call that "line"?

Answer 1

That line is called a crease.

crease
noun
a line on cloth or paper where it has been folded or crushed:

He ironed a crease down the front of each trouser leg.

Crease

Answer 2

A traveler's crease is the specific crease in the front of fancy slacks. As one website says:

The crease that runs vertically down the front of most slacks – pants that aren’t chinos or denim – is there to add sharpness and sophistication to your look. This fold, also known as a traveler’s crease, helps keep your pants neat when you hang them in a garment bag as well. You’ll typically find them on work, semi-formal, or formal pants.