Business Connectivity Services is a centralized infrastructure in SharePoint 2013 and Office 2013 that supports integrated data solutions. With Business Connectivity Services, you can use SharePoint 2013 and Office 2013 clients as interfaces into data that doesn’t live in SharePoint 2013 itself. For example, this external data may be in a database and it is accessed by using the out-of-the-box Business Connectivity Services connector for that database. Business Connectivity Services can also connect to data that is available through a web service, or data that is published as an OData source or many other types of external data. Business Connectivity Services does this through out-of-the box or custom connectors. The connectors, as the name implies, are the communication bridge between SharePoint 2013 and the external system that hosts the external data. For an overview of using OData in BCS from a developers perspective, see Using OData sources with Business Connectivity Services in SharePoint 2013 in the MSDN Library