Number of days allowed by a port authority to a ship to load or unload cargo without incurring demurrage or late charges. Lay days may be expressed as (1) Running days: consecutive days including weekends and holidays. (2) Working days: consecutive days excluding weekends and holidays. (3) Weather working days: days on which weather permits continuous work. Lay days begin to run when the vessel is berthed or when its arrival is recorded as arrived ship. Also called lay time.