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How many faces does an icosahedron have?

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Map of the Greco-Roman world highlighting the birthplaces of notable ancient mathematicians, marked with the pi symbol and labeled with their names. Cities such as Athens, Alexandria, Syracuse, and Miletus are shown around the Mediterranean, with modern country boundaries outlined. An inset provides detail for the region of Greece and western Anatolia. — geometry This map spans a millennium of prominent Greco-Roman mathematicians, from Thales of Miletus (c. 600 bce) to Hypatia of Alexandria (c. 400 ce).

An icosahedron is one of the five Platonic solids, which are regular polyhedra characterized by congruent faces and identical angles.12

An icosahedron has exactly 20 faces, each of which is an equilateral triangle. The name itself reflects this structure, as the combining form icosa- is derived from the Greek word for twenty.23