| term | meaning (click term for explanation in text) |
| all round light | light on a vessel that shines in a full circle (white, red or green) |
| collision, risk of | see risk of collision |
| COLREGS | another name for International Regulations for Prevention of Collision at Sea |
| constrained by draught | vessel restricted in the course she can follow because of the available depth of water |
| engaged in fishing | vessel which is actively engaged in fishing |
| fishing | see engaged in fishing |
| flashing light | light on a vessel that flashes with a frequency of 120 or more per minute |
| give-way vessel | vessel that is required to give way in a situation where there is a risk of collision |
| IMO | International Maritime Organisation |
| IRPCS | International Regulations for Prevention of Collision at Sea |
| masthead light | light on a vessel that shines white in a forward sector |
| mayday | codeword for distress; message of distress |
| not under command | vessel unable to manoeuvre because of some exceptional circumstance |
| overtaking | coming up from behind another vessel to go past it |
| port tack | sailing with the wind on the port side, or with mainsail set on the starboard side |
| restricted in ability to manoeuvre | vessel unable to manoeuvre because of her work |
| risk of collision | two vessels approaching one another on a constant bearing |
| sidelight | light on a vessel that shines red in port sector or green in starboard sector |
| stand-on vessel | vessel that is required to hold her course and speed in a situation where there is a risk of collision |
| starboard tack | sailing with the wind on the starboard side, or with mainsail set on the port side |
| steaming light | see masthead light |
| sternlight | light on a vessel that shines white in a sector astern |
| towing light | light on a vessel that shines yellow in a sector astern |
| traffic lane | defined lane in a traffic separation scheme for vessels proceeding in one direction |
| traffic separation scheme (TSS) | area marked on the chart where special IRPCS rules apply because of volume of shipping traffic |
| types of light | defined types of light on vessels (masthead light, sidelights, sternlight etc) |