2-dimensional (2D) figures
have height and width

They are commonly known as 
SHAPES

Here are some common shapes:

Squares = 4 sides
Circles = NO sides
Triangles = 3 sides

Polygons:
closed plane (2D) figures 
made from line segments
      triangles (3 sides)    quadrilaterals (4 sides)

pentagons   (5 sides)hexagons  (6 sides)

heptagons  (7 sides) octagons  (8 sides)

Remember:

Shapes are 2-dimensional figures.

Polygons are multi-sided shapes.