Office Web Apps Server is an Office server product that provides browser-based file viewing and editing functionality for Office files. Office Web Apps Server works with products and services that support WOPI, the Web app Open Platform Interface protocol. These products, known as hosts, include SharePoint 2013, Lync Server 2013, and Exchange Server 2013.
An Office Web Apps Server farm can provide Office services to multiple on-premises hosts, and you can scale out the farm from one server to multiple servers as your organization’s needs grow. Although Office Web Apps Server requires dedicated servers that run no other server applications, you can install Office Web Apps Server on virtual machine instances instead.