Final answer:
A Mooring Mark is an aid to navigation indicating where vessels can moor, with distinct light patterns (FlY (1) 4s) for identification at night or in poor visibility, and unique letters for differentiation.
Step-by-step explanation:
The Mooring Mark Meaning indicates that a particular mark is designated for the mooring of vessels. The term 'mooring' refers to the securing of a vessel to a fixed object such as a buoy, dock, quay, or the seabed, often by using ropes, cables, or anchors, for the purpose of keeping the vessel at a particular location.
The Lights: FlY (1) 4s aspect of the mooring mark refers to its light characteristics for navigation during low visibility conditions, such as at night or in fog. 'FlY' means the light flashes yellow, '1' denotes a single flash, and '4s' indicates the light pattern repeats every 4 seconds. This specific light pattern helps mariners identify the mooring mark from other navigational aids.
Regarding ID Types: Letters, this suggests that the mooring mark can be identified by specific letters, which are used to differentiate one mooring mark from another. This information can be critical when navigating busy or congested waterways where multiple mooring options exist.