The best term to describe \( \overleftrightarrow{GF} \) in this context is angle bisector.
Here's why: When Mere folded the paper so that point A was on top of point B, the fold creates an angle at point C where each side of the angle would be along the lines connecting C to A and C to B. The line \( \overleftrightarrow{GF} \) drawn through point C at an arbitrary angle would create angles on either side of it. If \( \overleftrightarrow{GF} \) divides this angle into two equal angles, then it is indeed functioning as an angle bisector.
If you were looking for terminology regarding a fold that intersects a line segment specifically, other terms might apply, but in the context provided, an angle bisector is the most relevant term.