Pentagon is a 5 sided polygon and the shape must be closed one.

When all the sides of the polygon are equal we get a regular pentagon. When the sides are not equal then the pentagon is irregular pentagon.
Regular and Irregular Pentagon

The pentagon has interior angles and exterior angles.
The angles formed at the vertex by joining the side segments lying inside the pentagon are called as interior angles.
Angles formed by extension of one of the side segment with adjoining segment and lying outside the enclosed area of the pentagon is called as exterior angle. In a regular pentagon, all the interior angles measure the same.

In the following figures we can see 5 interior angles marked with blue arcs.
The angles on outer side marked with red arcs are exterior angles. The pentagon has five exterior angles.
Angles of Pentagon