1) A deliberate misspelling of "historical" and "hysterical" to create a portmanteau, which means literally "very funny history" or "funny today, though it was serious at the time."
2) An extension of this meaning is to derisively imply that something today is garbage, of little importance, or no value — but might have "histerical value" in the future.
1) "The TV Show Dragnet is a histerical example of 1960s attitudes."
2) "I am keeping these videos of Trump speaking for their histerical value."
Free from traditional social or moral constraints; the opposite of inhibited.
Usage note: The vernacular "uninhibited" is grammatically incorrect as it contains a double-negative. The gentle urban speaker prefers the lesser-known, yet infinitely more refined, "hibited." See hibition.