A final solution to a situation, usually after much deliberation, and a final acceptance of that fact. It can be giving up on expecting someone to show up, or as it's typically used amongst The Mafia, a death sentence.
The simplest definition is: a ultimate, final acceptance. Period. Past all points or avenues of trying to change the situation. Gun at your head, you're done crying, he's not hearing you out. It is what it is. Get on with itmotherfucker!
Frank Sheeran: "Tony told the old man to tell me to tell you... 'it's what it is'"
Jimmy: "What it is?"
Frank: "It's what it is."
Jimmy: *sniffling* "They wouldn't dare"
or
Tim: "The pharmacy won't process my refill. I tried everything."
Nick: "Not even for tomorrow?"
Tim: "It is what it is. I'm out of ideas."
An all but lost phrase from the seventies era of ebonics, the closest contemporaryequivalent being, "What up?" WHAT IT IS is often a rhetorical question like, "How's it hanging?" or "What's going on?"
A) A phrase that seems to simply state the obvious but actually implies helplessness.
B) A phrase that seems to simply state the obvious but actually means "it will be what it is," as in "it ain't gonna change, so deal with it or don't." See also tough shit, oh well, cry me a river and tfb.