Definition
Progress
Progress is a liveness requirement for the critical section problem. If no process is in its critical section and one or more wish to enter, the selection cannot be postponed indefinitely. The system must continue doing work, not stuck in infinite negotiation. Progress guarantees the system is free from deadlocks regarding critical section entry.
Analogy
The Polite Doorway
Two people reach a doorway simultaneously and both endlessly insist the other go first (“After you!”, “No, after you!”). This fails progress. A valid solution ensures one eventually passes through.