IMPORTANT DEFINITIONS ABOUT CIRCLES

Circle : Set of points at the same distance to a point called center
Circumference : It is the full length of a circle . The complete distance around a circle
Center : It is the point equidistand to any of the points on a circle
Radius : it is the length of a line segment from the center to its perimeter 
Diameter : A line segment that passes through the center and conects two points of a circle . Its lengh is double than the radius
Chord : A line segment which conects two points of the circle not trough the center
Arc : Segment of a circle 
Tangent : Element which touch a circle in one point
Outer : Whwn an element doesn´t touch a circle in one point 
Inner : When an element is fitted inside teh circumference , or another element , being tangent or not
Concentric circles  They are circles with diferent radius but place in the plane sharing the center