Triangle !
There is no shape that is made up 3 sides that is not a triangle. Any shape that is made up of 3 sides is classified as a triangle no matter what shape or size it is.
A triangle as no other 2d shape can have 3 sides.
A triangle has 3 sides
A shape with 3 sides is a triangle.
A tripod would fit the given description
A shape with three sides is a triangle.
How about a triangle which is a 2 dimensional shape with 3 sides
3 sides
A triangle has 3 sides.
A 4 sided shape has 4 vertices whereas a 3 sided shape has 3 vertices.
Shape has fewer than 6 sides