They are polyhedra.
They are polygons and they have 3 or more sides
A polyhedran is a 3-dimentional figure that has sides that are polygons. A polygon is a 2-dimentional figure with straight sides, a closed side.
Pentagonal-Based Pyramid
it is a 3 dimentional triangle ... it can be a pyramid with 5 sides ... or one with four sides
it is a flat surface... the opposite of 3-dimentional.
There is no special name: they are polygons, as are shapes with 3 or 3 million sides.
Polygons are shapes with 3 or more sides
Triangles
Triangles have 3 sides.
A circle has no volume. Volume is only for 3-D shapes. A circle does not have volume because it is a 2 dimentional figure.A circle can only have circumfrance and area. Only a 3 dimentional figure can have volume. Mabye you are thinking about a sphere.
A triangle
A Triangle