What are set up time and hold time constraints? What do they mean? Which one is crucial for establishing maximum clock frequency of a circuit?

Set up time is the amount of time the data must be stable before the application of the clock signal, there as the hold time is the amount of time the data must be stable after the application of the clock. Setup time identifies maximum delay constraints; hold time is for minimum delay restrictions. Setup time is critical for estimating the maximum clock frequency.