desire line (di.ZYR lyn) n. An informal path that pedestrians prefer to take to get from one location to another rather than using a sidewalk or other official route.

Earliest Citation:

Study participants also drew charts of pedestrian traffic to take note of what are delightfully termed “desire lines”—paths actually made by walkers as opposed to those created on the drawing board.

—Thomas Frick, “Rebuilding Central Park,” Technology Review, August 1987

Source: Word Spy.