minimum-cost [perfect matching]
minimum-cost [traveling salesman tour]
[Eulerian graph] - graph (or multigraph) where every vertex has even degree
[Eulerian tour] - a tour (cycle) crossing every edge exactly once
[metric graph] - a complete graph with non-negative edge weights satisfying the triangle inequality
minimization problem, maximization problem, c-approximation algorithm
approximation-preserving reduction
maximal matching - matching not contained in any other matching
maximum matching - matching of maximum cardinality
VertexCover? - collection of vertices touching all edges
SteinerTree of a subset S of vertices - a tree containing the vertices in S, and possibly more.