Six degrees of Kevin Bacon: each "person" is a vertex (node), how they're connected (co-star? one directed another? dog sitter?) is an "edge", and the series of connections between you and Kevin Bacon is a path. If you can go from one person to Kevin Bacon, and then back to that one person without repeating any people in-between, that's a cycle.

Two sentences, but the second one is a segue to the more useful parts of graph theory if they are interested.