peering
termISP & telecom
Two networks exchanging each other's customer traffic directly, usually settlement-free - because both save on transit.
The handshake economy of the internet; disputes over it occasionally make headlines and lag spikes.
Peering is two networks exchanging traffic between their own customers directly, usually without payment, as distinct from transit where one pays another to reach the whole internet. The decision is commercial rather than technical.
Its practical effect is on path and performance. Traffic between two peered networks takes a short direct route; traffic that has to traverse transit may travel much further and cost both parties more. Peering disputes therefore show up as user-visible congestion on specific paths at specific hours, and they are resolved in commercial negotiation rather than by any protocol. Understanding this is why a slow connection to one specific service, at peak hours, from one specific provider, is often not a fault at all.