It is defined in terms of a mathematical game in which n cops try to capture a robber, who escapes along the edges of the graph.
The entanglement game[1] is played by n cops against a robber on a directed graph G. Initially, all cops are outside the graph and the robber selects an arbitrary starting vertex v of G. Further on, the players move in turn.
In each move the cops either stay where they are, or place one of them on the vertex currently occupied by the robber.
The robber must move from her current vertex, along an edge, to a successor that is not occupied by a cop.
If there is no free successor to which the robber can move, she is caught, and the cops win.