What are wait statistics?

Wait statistics summarize what SQL Server worker threads have been waiting for, such as storage I/O, locks, CPU scheduling, network activity, memory grants, or parallelism coordination.

They are one of the most useful tools for identifying broad performance bottlenecks. However, waits are symptoms, not diagnoses. A high wait category must be interpreted in the context of workload, time interval, baseline, and query behavior.

Instance-level waits accumulated since startup are often less useful than deltas measured over a representative problem period.