An unofficial path created as a consequence of active use caused by heavy traffic, usually representing the shortest or most easily navigated route between an origin and destination. Desire lines can be physical paths as well as paths to achieving particular outcomes in a system usability context (such as navigating websites or using a smartphone).
The term used this way dates back to 1946 by American transport planners planners to mean ‘a straight line from an origin to a destination’, and was subsequently picked up by urban planners, architects, and designers. (source)
Desire lines are not always a substitute for positive outcomes. Shortcuts can lead to faster but less healthy foods, multi-tasked but less engaged activities, and to-do list checkboxes but fewer accomplishments. Desire lines shows us the world that is, not the world that we would design, or even that we could design.