A Feature Collection is a JSON object that contains an array of features, where each feature is a JSON object with a geometry and a set of properties. A feature represents a spatially bounded entity, such as a point, line, or polygon, and its associated attributes. A Feature Collection can represent any number of features, and the features can be of different types.
A Feature Collection is often used to represent geographic data, and it is a common format used by web mapping libraries and services. For example, the OpenLayers library uses Feature Collections to represent vector data on a map. Feature Collections can be easily consumed and rendered by web mapping applications, and they can be easily transformed into other formats, such as GeoJSON, which is a standard format for geographic data in web mapping.
For more information on GeoJSON and Feature Collections, see the Wikipedia page.