inet0 - Juniper nomenclature for the IPv4 route table. One of several route tables that are created by the OS.
rib groups - stands for "routin information base" - this is a way within Junos to share route information across routing instances that have been configued. By default route data is not shared across instances.
routing instances - unique collection of routing tables, interfaces and routing protocol parameters - each routing instance operates independently.
virtual router - a type of routing instance - used for system virtualization - IE - to create an independent routing instance with its own interfaces and associated routing options (protocols, routes,...) NOTE - term is also used in the context of VRRP to refer to the logical router for gateway addressing.