It Is What It Is: The Idiomatic Expression Usage Guide

For when you want to say "that's just how it is" without actually saying it.

Usage:

When you want to convey the feeling of resignation, but still sound vaguely optimistic.
When you're feeling lazy, but still need to get the job done.
When you're trying to sound wise, but secretly have no idea what you're talking about.

Common uses:

As a response to "what do you mean by that?"
When someone asks you to explain something, but you're not really sure how it works.
As an excuse to get out of a meeting or commitment