A linear pair of angles is a pair of adjacent angles formed when two lines intersect each other at a single point. The term "linear" refers to the fact that the angles are arranged along a straight line. Two angles are said to form a linear pair if they meet the following conditions:

• They are adjacent angles.
• Their non-common arms are opposite rays and form a straight line.

Properties of a linear pair of angles include:

• The angles in a linear pair are supplementary, meaning they add up to $180^\circ$.
• A linear pair of angles are always adjacent angles.
• A linear pair of angles always form a straight line.
• Two angles forming a linear pair have a common vertex and a common arm. Their non-common sides are opposite rays that form a line.

The linear pair postulate states that if two angles form a linear pair, they are supplementary. However, the converse of this postulate is not true. This means that if two angles are supplementary, they do not necessarily form a linear pair of angles.