Circle

Circle[{x,y},r] represents a circle of radius r centered at {x,y}.

Circle[{x,y}] gives a circle of radius 1. 

Circle[{x,y},{rx,ry}] gives an axis-aligned ellipse with semiaxes lengths rx and ry.

Circle[{x,y},…,{θ1,θ2}] gives a circular or ellipse arc from angle θ1 to θ2.

Please visit the official Wolfram Language Reference for more details and examples on core symbols.