A measurement of how tired you are. Also can be used to denote how far away from dropping dead asleep you are.
(0 - minimum; 100 - maximum)

Mathematically:

{1 - (Ability to stay awake and do whatever you are doing at that point of time)/(Ability to keep doing whatever you are doing after 12 hours of dreamless sleep)}x100

where units of Ability are user-defined as long as the unit is constant in the numerator and denominator.

A Tiredness Quotient (TQ) of 0 would mean you are not tired at all or you are wide awake with no hint of fatigue.

A TQ of 100, on the other hand, would cause you to fall sleep involuntarily.

In some countries people may refer to this as Tiredness Index or Fatigue Index or Fatigue Quotient.

When you eat dirt for the first time and leave your family to build a shack in the woods