The term 'Call at Sea' refers to the various signals used by ships to communicate with each other. The most common signals are 'AVAST' (5 letters), 'AHOY' (4 letters), and 'SOS' (3 letters). AVAST is a nautical command meaning 'STOP' or 'CEASE'. AHOY is a traditional greeting used to hail a ship or a person on board. SOS is an internationally recognized distress signal used to indicate that a vessel is in need of immediate assistance.