An alley is a transportation corridor for road vehicles which crosses a city block, providing access to parking, back yards, garbage collection, etc., and which is not part of a general transportation route. Alleys are generally either not connected with each other, or the connections are rarely used to join them into a single route.

The corridor gives access to the interior or rear of the block. Parking and refuse collection are examples of that access function.

Connections to other alleys may exist without forming a commonly used through route. Its local access role distinguishes the alley from the wider street network.