Topology
Beginner
The pattern of who is wired to whom.
Novice
The shape of a network: which chips (or switches) are connected by links. Rings, meshes, tori and switched stars are common patterns.
Expert
A graph whose properties (degree, diameter, bisection bandwidth, path diversity) bound latency and throughput for each traffic pattern, and whose regularity decides which collective algorithms map onto it without contention.