A matching in a graph is a set of edges that are pair-wise non-adjacent. IOW, each node involved in the matching appears in only one edge.
Now I am wondering is there a ``generalized'' concept of matching, such that it still refers to an edge-set, and each vertex involved can appear in at most $k$ edges in this edge-set, where $k \ge 2$ is a pre-specified positive integer.
If such concept does exist, what are some interesting and representative problems studied for that?