Circles, Arcs and Lines 

You can divide a circle into smaller portions. A part of a circle is called an arc and an arc is named according to its angle. Arcs are divided into minor arcs , major arcs and semicircles .
A line that "just touches" the circle as it passes by is called a Tangent. ... A line segment that goes from one point to another on the circle's circumference is called a Chord. If it passes through the center it is called a Diameter. And a part of the circumference is called an Arc.