A pentadecagon is a polygon with fifteen sides and fifteen angles. The term comes from the Greek words "penta," meaning five, and "deca," meaning ten, combined to indicate fifteen. Each internal angle of a regular pentadecagon measures 156 degrees, and the sum of all internal angles is 2,340 degrees. Pentadecagons can be found in various fields, including mathematics and architecture. They are part of the study of geometry, which explores shapes, sizes, and properties of space. Regular pentadecagons have equal side lengths and angles, making them a subject of interest in tessellation and design.