load line

A load line is a mark on a ship's hull indicating the maximum depth to which the vessel may be safely submerged when loaded with cargo.

Different lines account for varying water conditions—fresh versus salt water, summer versus winter seas.

Also called a Plimsoll line or Plimsoll mark after the British reformer who mandated them.

In electronics, a load line is a graph showing how a component's voltage and current relate under different loads.