Plain English Meaning

A starting line you measure everything from. For weight and balance, it's the zero point the manufacturer picks on the aircraft, and every item's position is described as a distance forward of or behind that line.

Full Definition

A fixed reference point, line, or surface from which measurements are taken. In aircraft weight and balance, the datum is an imaginary vertical plane established by the manufacturer, from which all longitudinal distances (called arms) are measured to determine the location of the center of gravity.

Context Anchor

Seen in weight-and-balance calculations, aircraft records, maintenance manuals, and aircraft drawings.

Derivation

From Latin datum, meaning 'something given.' In measurement, it's the value or point that is 'given' as the starting , so every other measurement is taken from it.