- REST – is an architecture of how to send messages over HTTP.
- OData (v4) – is a specific implementation of REST, really defines the content of the messages in different formats (currently I think is AtomPub and JSON). ODataV4 follows rest principles.
For example, asp.net people will mostly use WebApi controller to serialize/deserialize objects into JSON and have javascript do something with it. The point of Odata is being able to query directly from the URL with out-of-the-box options.