The widespread interest in provider-provisioned Virtual Private Network (VPN) solutions lead to memos proposing different and overlapping solutions. The IETF working groups (first Provider Provisioned VPNs and later Layer 2 VPNs and Layer 3 VPNs) have discussed these proposals and documented specifications. This has lead to the development of a partially new set of concepts used to describe the set of VPN services. To a certain extent, more than one term covers the same concept, and sometimes the same term covers more than one concept. This document seeks to make the terminology in the area clearer and more intuitive.