The handful of metrics that tell you if the business is actually working.
KPIs are the specific numbers you track to know whether you're winning. Not all metrics are KPIs, that's the point. A KPI is a metric tied directly to a goal. For a SaaS company, KPIs might be MRR, churn, CAC, LTV. For a restaurant: revenue per seat, food cost %, table turn time. Picking the right 3-5 KPIs is harder than it sounds.
If everything is a KPI, nothing is. Teams with 20 'critical' dashboards are teams with no priorities. Pick the five that actually move decisions and ignore the rest. Your KPIs should determine what you do this week.