OpenStreetMap (OSM) is an application that uses an open geographic database which is updated and maintained by a community of volunteers via Open collaboration.
OpenStreetMap is freely licensed under the Open Database License and it's commonly used to make electronic maps, turn-by-turn navigation, assist in humanitarian aid and data visualisation. OpenStreetMap uses its own topology to store geographical objects which can then be exported into other GIS file formats.
The whole project started in 2004, when Steve Coast founded the base project, initially focusing on mapping the United Kingdom. In April 2006, the OpenStreetMap Foundation was established to encourage the growth, development and distribution of free geospatial data and provide geospatial data for anybody to use and share. The turning point came in 2012, when Google Maps charged for its services. In response, several prominent services switched to using OpenStreetMap and other competitors.
Map features range in scale from international boundaries to hyperlocal details such as shops and street furniture. Although historically significant features and ongoing construction projects are routinely included in the database, the project's scope is generally limited to the present day, as opposed to the past or future.
In general, every map object is modelled as one of three geometric primitives:
Every feature, or object can also holds its own metadata. Each object contains key-value pairs, called tags, that identify and describe the feature. In addition, due to its high level of coverage, timeliness and detail, OSM often performs better than commercial or government mapping services.
OpenStreetMap data and derived tiles were originally published under the Creative Commons Attribution-ShareAlike licence (CC BY-SA) with the intention of promoting free use and redistribution of the data. Currently, all data added to a project must be licensed under the Open Data Commons Open Database License (ODbL), which in practice means that "©OpenStreetMap Contributors" with link to ODbL copyright page as attribution requirement is used on the your site.
The map data can be edited from a number of editing applications that provide aids including satellite and aerial imagery, street-level imagery, GPS traces, and photo and voice annotations. So feel free to sign up and help keep OSM up to date in your area. Or you can try plotting different data on the map, or create your own editor, e.g. using the Leaflet library.