What is meaning of Laycan?

Laycan is an abbreviation for the ‘Laydays and Cancelling Date’ clause in a charter party. This clause defining the time window in which the charterers are obliged to accept the vessel in the loading port.

If the vessel arrive before the first date agreed, the vessel has probably to wait.
If the vessel  arrive too late the charterers are entitled to not accept the vessel (cancelling date)