Definition:Concyclic Points

Definition
A set of $4$ or more points $S = \set {P_1, P_2, \ldots, P_n}$ is concyclic if they all lie on the circumference of a circle.


 * Concyclic.png

In the above diagram, points $A, B, C, D$ are concyclic, as they all lie on the circumference of the circle centered at $O$.

Also see

 * Vertices of Regular Polygon are Concyclic


 * Three Points Describe a Circle, demonstrating that any $3$ non-collinear points always lie on the circumference of a circle, which is why the definition specifies a set of $4$ or more points