The metre is defined in a similar manner, taking the distance from the North Pole to the Equator as baseline.
It's certainly not the current definition, which is the distance light travels in a vacuum in 1/~300,000,000 of a second. (A nice, handy yardstick, eh?).
I remember having to remember the SI unit definitions for A-Level Physics - the best, I think, was the amp, which is "that constant current which when maintained in two straight parallel perfect conductors of infinite length, positioned one metre apart in a vacuum, induces a force of 2×10
−7 newtons per metre length of each on the other." (for which, also see the definition of 'metre', and of 'kilogram', 'metre' and 'second' to understand the derived unit 'newton'. It's useful, because everyone has ready access to caesium-133, infinitely long conductors in vacuums, and Parisian kilograms.
)