A more thorough explanation:

Definition: A load line is a mark on the side of a ship that indicates the depth to which the ship can be safely loaded in different waters and weather conditions. It is also the depth to which a ship will sink when it is safely loaded in salt water.

Load lines are important because they help prevent ships from being overloaded and sinking. In the past, ship owners would often overload their ships to make more money, which put the lives of the crew and passengers at risk. Load lines were established to ensure that ships are loaded safely and to prevent accidents at sea.

Load lines are usually marked on the side of a ship with a series of lines and letters. The letters indicate the type of water the ship is in (salt water or fresh water) and the lines indicate the maximum depth to which the ship can be loaded in different conditions.

For example, a ship may have load lines marked with the letters "TF" for tropical fresh water and "TS" for tropical salt water. The lines may be marked with numbers that indicate the maximum depth to which the ship can be loaded in calm water, rough water, and other conditions.

Load lines are required by law in most maritime countries and must be cut and painted amidships. They are an important safety feature that helps ensure the safe operation of ships and the protection of the crew and passengers.