A circumcircle is a circle that passes through all the vertices of a polygon, particularly a triangle. The center of this circle is called the circumcenter, which is the point where the perpendicular bisectors of the triangle's sides intersect. The radius of the circumcircle is known as the circumradius. In the case of a triangle, the circumcircle is significant in various geometric properties and theorems. For example, the circumcircle can help determine the relationship between the triangle's angles and sides, as described by Euclid's geometry. It is also used in constructions and proofs involving triangles and polygons.