is a REST-based protocol for querying and updating data and is built on standardized technologies such as HTTP, Atom/XML, and JSON.
It is different from other REST-based web services in that it provides a uniform way to describe both the data and the data model.
Vtiger provides an entry point to access data in OData format.
User can hit the OData URL and provide credentials to fetch information from any module
For example, To fetch data from Contacts module -instance_url/restapi/V1/OData/Pull/odata.svc/Contacts
Refer : OData feed