OData is a Web protocol for querying and updating data, applying and building on Web technologies such as HTTP, Atom Publishing Protocol (AtomPub), and RSS (Really Simple Syndication) to provide access to information from a variety of applications. It is easy to understand and extensible, and provides consumers with a predictable interface for querying a variety of data sources.
All the information relevant to the OData it is explained into the KBA "2595454 HOW TO: Add, Activate and Maintain OData Services" also into the "SAP Help" we provide more information about it , please check the link Activate and Maintain Services
If the SAP Cloud Platform OData Provisioning it is used here it is a good overview from the SAP documentation
Into the link wiki SAP Fiori - OData and Gateway you can find information about how to extend and develop Odata.