Final answer:
The base SI unit for length is the meter (m). Other metric units of length, such as the centimeter and millimeter, are derived from the meter.
Step-by-step explanation:
The base SI unit for length is the meter (m).
The meter was originally defined as 1/10,000,000 of the distance from the North Pole to the equator. However, it is now defined as the distance light in a vacuum travels in 1/299,792,458 of a second.
Other metric units of length, such as the centimeter and millimeter, are derived from the meter.