Key characteristics:
* Adjacent: They share a common side and vertex.
* Supplementary: The sum of their measures is 180 degrees.
* Form a straight line: The non-common sides of the angles extend in opposite directions to form a straight line.
Example:
Imagine a straight line. Now, draw a ray starting from a point on that line. This ray divides the straight line into two angles. These two angles are a linear pair because they share a common side (the ray) and their non-common sides (the two parts of the straight line) form a straight line.
Important note: The definition of a linear pair does not require the two angles to be congruent.