A quintessentially American East Coast colloquialism that is meant as a sort of passive acceptance of a situation that is not favorable but also cannot be changed (or at least not right away). It can be used in any context, although usually it refers to an illness, injury, stroke of bad luck financially, romantic trouble, etc. It should never be used as a means to an end in an actual intellectual comversation. Also known as: What will be will be. Suck it up. Deal with it.
"Landlord bumped my rent up... oh well, we don't have a lease agreement. Eh, it is what it is."
::after a long perios of obsessively analyzing what went wrong in a toxic relationship; finding oneself depressed and overwhelmed by the details of it all; an acceptance (these are usually prefaced by a weighted sigh):: "It is what it is."