What is a ten sided shape called?

a decagon:

A decagon is a polygon with ten sides, ten vertices, and ten angles. It is often depicted as a regular decagon, meaning all sides are equal in length and all angles are of the same measure (144 degrees). A decagon can also be irregular, where the sides and angles may vary in size. The sum of the interior angles in a decagon is 1440 degrees, and the exterior angles add up to 360 degrees. Decagons are often seen in architecture, such as in the design of some buildings, and in nature, such as in the shape of some fruits or flowers.