VM or Process – a JBossAS instance running Teiid.  

Host – a machine that is “hosting” one or more VMs.

Service – a subsystem running in a VM (often in many VMs) and providing a  related set of functionality
In addition to these main components, the service platform provides a core set of services available to applications built on top of the service platform.  These services are:

Session – the Session service manages active session information.

Buffer Manager – the Buffer Manager service provides access to data management for intermediate results.

Transaction – the Transaction service manages global, local, and request scoped transactions.  See also the documentation on Transaction Support.