It's called an Octagon.
otagon
A plane figure with eight sides is an octagon.
polygon
If they are straight sides, then a polygon. Otherwise, simply "a closed plane figure with 3 or more sides".
A plane figure is a geometric shape. A plane figure is known as a 2-dimensional shape because it has only length and breadth. The thickness of the plane figure is zero. Any shape that is drawn on paper is known as a plane figure. In the real world, there is no object that represents a plane figure.
hendecagon
A plane figure with eight sides is an octagon.
An octagon is a plane figure. It has eight sides, but no real base.
It is a dodecagon
A two-dimensional figure is a polygon. The eight sides means that it uses the prefix octa- (meaning eight) to form the name octagon.
decahedron
A expample of a plane figure with 6 sides and 6 vertices is called a hexagon. hex means 6.
It is a polygon that is a closed plane figure with 3 or more straight lines.
A plane figure with a googol sides is called a googolgon.
The polygon (figure) that contains 8 sides is called an "octagon".
A polygon.
An eight-sided plane figure is an octagon. If the sides are all the same length, and the angles are all equal, it is a regular octagon.
A 12-sided polygon is called a dodecagon. See this website for more names: http://mathforum.org/dr.math/faq/faq.polygon.names.html a plane figure 12 sides