A private connection between two VPCs (in the same project or different projects and organizations) so their resources communicate over internal IPs. Each VPC keeps its own administration.
Two classic ACE rules: peering is not transitive (A-B and B-C do not connect A with C), and the networks’ IP ranges cannot overlap. It cannot connect on-premises networks.
VPC Network Peering is a concept that can show up on the exam. Check the full guide to see it in context.