A circuit in graph theory is a path that starts and ends at the same vertex with no other repeated vertices. It is a closed loop in a graph where each edge is used exactly once.
Path: A sequence of edges which connect a sequence of vertices.
Hamiltonian Circuit: A circuit that visits each vertex exactly once before returning to the starting vertex.
Eulerian Circuit: A circuit that traverses every edge of the graph exactly once, starting and ending at the same vertex.