"Masthead light" means a white light on the centreline of the vessel showing from right ahead to 22.5 degrees abaft the beam on either side of the vessel.
"Sidelights" means a green light on the starboard side and a red light on the port side each showing from right ahead to 22.5 degrees abaft the beam on its respective side. If the vessel is less than 20 metres (66 ft) long, the sidelights may be combined in one fixture carried on the centreline of the vessel.
"Sternlight" means a white light placed as nearly as practicable at the stern showing 67.5 degrees from right aft on each side of the vessel.
"Towing light" means a yellow light having the same characteristics as a "sternlight" defined above.
"All-round light" means a light visible from 360 degrees of the horizon.
"Flashing light" means a light flashing faster than 120 flashes per minute.
Are you trying to figure out what lights you need on your boat? The easy way is based on length. Sailboats, powerboats, Here are some good resources:
International Regulations for Preventing Collisions at Sea