Final answer:
The term 'MIL' represents a unit of length equal to 0.001 inches and is the correct answer. In contrast, the metric system uses millimeters as the smallest common metric unit of length, where 1000 mm is equal to 1 meter.
Step-by-step explanation:
The word that represents a unit of length equal to 0.001 inches is 'MIL'. This unit is not part of the metric system but is used in the United States for measuring very small distances. It is often used in engineering and manufacturing to specify thicknesses of various materials, including plastics and metals.
The confusion may arise from the metric system, where 'milli-' indicates 1/1000 of a base unit, so 1000 mm is equal to 1 meter (1m). Similarly, there are 10 millimeters in a centimeter (10 mm in 1 cm), and the smallest common metric unit of length is indeed a millimeter (mm). However, 'MIL' is specifically used for inches, where 1 MIL = 0.001 inches.