A transversal is a line that intersects two (or more) lines.

In illustration one below, LINE 1 is a transversal of LINE 2 and LINE 3.

In illustration two above:

• LINE 1 is a transversal of LINE 2 and LINE 3
• LINE 2 is a transversal of LINE 1 and LINE 3
• LINE 3 is a transversal of LINE 1 and LINE 2

Usually angles associated with a transversal are studied. Common examples of these are:

• opposite angles
• corresponding angles
• alternate angles
• angles on the same side of the transversal
• interior angles
• exterior angles