What is the meaning of It_is_what_it_is?

That's life; expressing resignment to a situation or set of circumstances, usually without complaint

Let it be; accept the fact and let the matter rest.

  1. Who cares?; I don't care.

Who cares?; I don't care.

Used other than figuratively or idiomatically: see it, is, what, it, is. This object has its own distinct nature; this object is itself.

Source: wiktionary.org