The inputs are a graph, G, and a list of terminal vertices.  The goal is to create a subtree that spans all the terminal vertices.  The non-terminal vertices may or may not be included in the subtree.  There will always be such a subtree.

This is similar to minimal spanning tree, but it's harder because not all vertices have to be included.  It's permitted to have weighted graphs for this problem, in which case you should look for the minimum tree that spans all the terminal vertices.

Here's a video: https://youtu.be/BG4vAoV5kWw