Train track (mathematics)
In the mathematical area of topology, a train track is a family of curves embedded on a surface, meeting the following conditions: 1. * The curves meet at a finite set of vertices called switches. 2. * Away from the switches, the curves are smooth and do not touch each other. 3. * At each switch, three curves meet with the same tangent line, with two curves entering from one direction and one from the other. The main application of train tracks in mathematics is to study laminations of surfaces, that is, partitions of closed subsets of surfaces into unions of smooth curves. Train tracks have also been used in graph drawing. (Wikipedia).
