Core JXTA Concepts

Peer - a virtual communications point. Application node, gateway, router, rendezvous or combination.

Peer Group - A way to group peers and advertise services. (Logical VPN?) Groups can limit membership.

Endpoint - Basic addressing method used by JXTA. An address of a peer that implements a specific protocol. A peer can have multiple endpoints and thus can be communicated to via different protocols (HTTP, TCP, BEEP, etc).

Pipe - A virtual connection between peers. Pipes are an abstraction used to hide how many peers are used to establish a connection (routers etc). Pipes can also be self-healing and reroute around an original peer. Pipes can communicate over multiple protocols and usually use multiple endpoints.
 
Advertisement - An XML document that describes a JXTA message, peer, peer group or service. Advertisements use rendezvous peers as virtual "billboards".

Message - An XML or XML-binary payload.