Definition:Arc


 * Graph theory: An arc of a directed graph is a line, with a directional arrow, that joins one vertex to another.


 * Geometry: An arc is a specific part of a general curve. Particular usages:
 * Arc of a Circle: any part of its circumference;
 * Arc of a Cycloid: one of the parts of a cycloid between two cusps.


 * Topology: An arc from $a$ to $b$ in a topological space is a continuous injection $f: I \to T$ such that $f \left({0}\right) = a$ and $f \left({1}\right) = b$.