A physical state where you are more adept at tasks which are difficult when too sober or too drunk (e.g. bowling, pool, beer pong, hitting on the opposite sex)
See:
Equilibrium - a state of balance
inebriated - made drunk, intoxicate
I always start out sucking at beer pong, but there is that magic time in the night when I hit equinebrium and I just start making cups.
A person who is very knowledgeable and enthusiastic about miniature toy horses, often in times of depression, young wizards will turn to it as an escape from reality.
Harry in a spiral of depression, turns to the escape of the world of Miniature Equine Aficionada.
This was practice was common among cowboys and indians alike but is thought to have originated on the Stepps of Northern Asia by the Mongolians who's affection for horses is legendary.
I banged that dead horse like a cheap screen door and she would have loved it if she were not dead as a doornail.