The Open Data Protocol (OData) is a Web protocol for querying and updating data that provides a way to unlock your data and free it from silos that exist in applications today. OData does this by applying and building upon Web technologies such as HTTP, Atom Publishing Protocol (AtomPub) and JSON to provide access to information from a variety of applications, services, and stores. The protocol emerged from experiences implementing AtomPub clients and servers in a variety of products over the past several years. OData is being used to expose and access information from a variety of sources including, but not limited to, relational databases, file systems, content management systems and traditional Web sites.
Note however, that OData is a Microsoft project. They state:
The name Open Data Protocol was chosen to make it clear that the protocol is intended to align with the Open Data movement and that we are fully committed to ensuring that the protocol remains as open as possible.
Here’s a list of articles and videos with more details on this project. You may be hearing some debate in the open source community about OData in the future, including a talk at the Open Source Bridge conference in Portland, OR this summer. These materials will give you some background on the topic.