In the mathematical discipline of graph theory, a graph C is a covering graph of another graph G if there is a covering map from the vertex set of C to the vertex set of G. A covering map f is a surjection and a local isomorphism: the neighbourhood of a v vertex in C is mapped bijectively onto the neighbourhood of f(v) in G.
The term lift is often used synonymous for a covering graph of a connected graph.
In graph theory, a covering graph may also refer to a subgraph that contains either all edges (edge cover) or all vertexes (vertex cover).
The combinatorial formulation of covering graph is immediately generalized to the case of multigraph. If we identify a multigraph with a 1-dimensional cell complex, a covering graph is nothing but a special example of covering spaces of topological spaces, so that the terminology in the theory of covering spaces is available; say covering transformation group, universal covering, abelian covering, and maximal abelian covering.[1]