A tetrahedron.
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tetrahedron
Isosceles TetrahedronA solid with four faces is a tetrahedron. Each of the faces is a triangle. If all the triangles are congruent, you have an isosceles tetrahedron.
Rectangles are plane (2-dimensional) polygons. Only solid (3-dimensional) polyhedrons have faces.
tetrahedron
A rectangular pyramid (four-sided base) has 5 faces and 5 vertices.