A greenway is usually a shared-use path along a strip of undeveloped land, in an urban or rural area, set aside for recreational use or environmental protection. Greenways are frequently created out of disused railways, canal towpaths, utility company rights of way, or derelict industrial land. Greenways can also be linear parks, and can serve as wildlife corridors. The path's surface may be paved and often serves multiple users: walkers, runners, bicyclists, skaters and hikers. A characteristic of greenways, as defined by the European Greenways Association, is "ease of passage": that is that they have "either low or zero gradient", so that they can be used by all "types of users, including mobility impaired people".

In Southern England, the term also refers to ancient trackways or green lanes, especially those found on chalk downlands, like the Ridgeway.

Greenways are vegetated, linear, and multi-purpose. They incorporate a footpath and/or bikeway within a linear park. In urban design, they are a component of planning for bicycle commuting and walkability. The British organisation Sustrans, which is involved in creating cycleways and greenways, states that a traffic-free route "must be designed on the assumption that everyone will use it", and measures taken "to assist visually and mobility impaired users".

The American author Charles Little in his 1990 book, Greenways for America, defines a greenway as:

A linear open space established along either a natural corridor, such as a riverfront, stream valley or ridgeline, or overland along a railroad right-of-way converted to recreational use, a canal, scenic road or other route. It is a natural or landscaped course for pedestrian or bicycle passage; an open-space connector linking parks, nature reserves, cultural features, or historic sites with each other and with populated areas; locally certain strip or linear parks designated as parkway or greenbelt.

The term greenway comes from the green in green belt and the way in parkway, implying a recreational or pedestrian use rather than a typical street corridor, as well as an emphasis on introducing or maintaining vegetation, in a location where such vegetation is otherwise lacking. Some greenways include community gardens as well as typical park-style landscaping of trees and shrubs. They also tend to have a mostly contiguous pathway. Greenways resemble linear parks, but the latter are only found in urban and suburban environments.

The European Greenways Association defines it as

Communication routes reserved exclusively for non-motorized journeys, developed in an integrated manner which enhances both the environment and quality of life of the surrounding area. These routes should meet satisfactory standards of width, gradient and surface condition to ensure that they are both user-friendly and low-risk for users of all abilities.