Wikipedia
OpenStreetMap (OSM) is a collaborative project to create a free editable map of the world. Two major driving forces behind the establishment and growth of OSM have been restrictions on use or availability of map information across much of the world and the advent of inexpensive portable satellite navigation devices. OSM is considered a prominent example of volunteered geographic information.
Created by Steve Coast in the UK in 2004, it was inspired by the success of Wikipedia and the preponderance of proprietary map data in the UK and elsewhere. Since then, it has grown to over 2 million registered users, who can collect data using manual survey, GPS devices, aerial photography, and other free sources. These crowdsourced data are then made available under the Open Database Licence. The site is supported by the OpenStreetMap Foundation, a non-profit organisation registered in England and Wales.
Rather than the map itself, the data generated by the OpenStreetMap project are considered its primary output. The data are then available for use in both traditional applications, like its usage by Craigslist, OsmAnd, Geocaching, MapQuest Open, JMP statistical software, and Foursquare to replace Google Maps, and more unusual roles like replacing default data included with GPS receivers. OpenStreetMap data have been favourably compared with proprietary datasources, though data quality varies worldwide.