Transversal –
A transversal is a straight line that intersects two or more lines in a plane. In the figure the transversal EF intersects the two lines AB & CD at the points P & Q respectively.
The angles formed at the point P are ∠APE, ∠BPE, ∠APQ and ∠BPQ. The angles formed at the point Q are ∠CQP, ∠DQP, ∠CQF and ∠DQF.
These angles, labeled 1 to 8 for convenience, are called –
Exterior Angles - ∠4, ∠3, ∠5, and ∠6
Interior Angles - ∠1, ∠2, ∠8, and ∠7
Alternate Angles – The pairs ∠1, ∠7 and ∠2, ∠8
Corresponding Angles – The pairs ∠1, ∠5; ∠2, ∠6; ∠3, ∠7; and ∠4, ∠8
Co-interior Angles – The pairs ∠1, ∠8 and ∠2, ∠7