Minimum spanning trees are networking graphs which have no closed circuits but connect every point to another so that one node on the network is accessible from any other node on the network, even if the route between them is long or goes through over nodes. A typical problem which requires finding the minimum spanning tree is cabling a number of houses to a single service. However, minimum spanning trees are not permitted to have a "hub" edge (in the style of a hub computer network) which is not connected to any nodes, only edges; all edges must have a node at both ends.
There are two main algorithms for finding minimum spanning trees, Prim's algorithm and Kruskal's algorithm. Both are greedy algorithms.