A square and a rectangle each have 4 sides and 4 angles. The only difference between them is that a square is a rectangle with equal sides. Both have 4 90 degree (right) angles.

A triangle has 3 sides and 3 angles. The angles of a triangle always add up to 180 degrees.

The closest thing a circle has to a side is the circumference (the circle itself). It also has an area (the space inside the circle) and a radius and diameter. The diameter is the distance from one side of the circle to the other, passing through the midpoint. The radius is half that distance – from the midpoint to the circumference. The “angle” of a circle is 360 degrees – all the way around.