Definition
Cone
A right circular cone has one circular base and a curved surface meeting at one apex.
What it means
Imagine a stack of circular slices. The bottom slice is the largest, each slice above it is smaller, and the stack narrows until it reaches one point.
Remember it
One circle below, one point above.
Example
A solid has a circular base of radius 3 cm and an apex 4 cm directly above the base centre. Its curved side narrows evenly to that apex, so it is a right circular cone.
Watch for
A pyramid is not a cone because a pyramid has a polygon base and flat triangular side faces.
Common mix-up
The base is flat, but the side is one curved surface rather than a ring of flat faces.
Exact meaning
On this page, cone means a right circular cone: a solid with a circular base and an apex directly above the base’s centre, with a curved surface joining the base circle to the apex.