The Spirit of Deerpark is a spirit that was sealed away, only to be cast into a mortal worthy of his power. The Spirit of Deerpark is the spirit of a man lost to insanity, and is tameable only by the mortal he resides in.

Briefly, "the realization that each random passerby is living a life as vivid and complex as your own." Originally from the Dictionary of Obscure Sorrows, which has a lot more beautiful neologism definitions like this you might enjoy.