The interior of a pentagon has five angles totaling 540 degrees. In a regular pentagon – a polygon with five congruent sides and five congruent angles – each angle is 108 degrees. Each exterior angle of a regular pentagon is 72 degrees.
A pentagon can be either concave or convex. Concave pentagons have at least one internal angle greater than 180 degrees. This means the angle points inward on the pentagon. Convex polygons do not have any internal angles greater than 180 degrees.
To qualify as a pentagon, a polygon must have five straight sides connected to each other. If it's not a closed shape, it's not a pentagon even if it has five sides.