JSON (JavaScript Object Notation) is a lightweight data-interchange format.

JSON (JavaScript Object Notation) is an open standard data format used to transmit data objects. JSON's data objects consist of attribute-value pairs, and while initially derived for JavaScript, JSON is language-independent, and the most popular alternative/successor to XML. Code for parsing and generating JSON data is readily available in a large variety of programming languages.
.json is JSON's filename extension.

GeoJSON is an open standard format for encoding collections of simple geographical features along with their non-spatial attributes using JavaScript Object Notation. The features include points (therefore addresses and locations), line strings (therefore streets, highways and boundaries), polygons (countries, provinces, tracts of land), and multi-part collections of these types. GeoJSON features need not represent entities of the physical world only; mobile routing and navigation apps, for example, might describe their service coverage using GeoJSON.

The GeoJSON format differs from other GIS standards in that it was written and is maintained not by a formal standards organization, but by an Internet working group of developers.

A notable offspring of GeoJSON is TopoJSON, an extension of GeoJSON that encodes geospatial topology and that typically provides smaller file sizes.

JSON-LD (JSON for Linking Data) is another flavor of JSON in the form of a lightweight Linked Data format. JSON-LD was created so it is easy for humans to read and write, based on the already successful JSON format and providing a way to help JSON data interoperate at Web-scale. JSON-LD is an ideal data format for programming environments, REST Web services, and unstructured databases (like CouchDB and MongoDB).