Queue number

A de Bruijn graph. With the vertex ordering shown, the partition of the edges into two subsets looping around the left and right sides of the drawing is a 2-queue layout of this graph.

In the mathematical field of graph theory, the queue number of a graph is a graph invariant defined analogously to stack number (book thickness) using first-in first-out (queue) orderings in place of last-in first-out (stack) orderings.