What is Scrum of Scrums?
Scrum of scrums scales coordination: each team sends a representative to a regular cross-team standup focused on dependencies and integration — what did your team do that affects others, what will it do, what's blocking between teams. It's the lightest scaling mechanism that works, and the first one to try before adopting a heavyweight framework.
Kept sharp, it's 15 minutes about interfaces; gone stale, it's a status meeting wearing agile clothes.
Worked example
Four teams build one marketplace. At Tuesday's scrum of scrums, payments' rep mentions a checkout-API contract change shipping Thursday; catalog's rep flags that their team consumes it and hasn't migrated. Thirty seconds of cross-team talk just prevented a broken Friday build — the exact collision class that single-team standups structurally cannot catch.