Two line segments are congruent if ________.

Congruence is the term used to define an object and its mirror image. 

Two objects or shapes are said to be congruent if they superimpose on each other. Their shape and dimensions are the same. In the case of geometric figures, line segments with the same length are congruent and angle with the same measure are congruent. 

If the lengths of two line segments are equal, they are said to be congruent. 

They may or may not align with an axis or a plane position at the same angle, as shown below.