It's entered our political lexicon, and you and I are talking about it, so I think it's gained word-status. It's a brand new concept which describes a real problem, but it has already been rhetorically abused beyond belief (much like the concept of "fake news," which instantly became right-wing shorthand for describing legitimate news outlets). That is what this set of memes is about.
The basic formula is this: "Let's debate X." "Well, what about Y..." It's a way of changing the subject rather than answering, and it sets up false equivalencies.
The classic example is Putin being asked about Russian human rights abuses, and responding with, "Well, what about the United States, they did XYZ..."
SOMETIMES, HOWEVER -- the whataboutism is warranted. Like when someone tells me I am being disrespectful for mocking Trump's hair, and I respond with, "Well what about Trump himself, he routinely denigrates the disabled/Mexicans/liberals/veterans/political opponents/what-have-you."
If the topic you are redirecting the focus toward is really more serious and noteworthy, then it's a legitimate rhetorical move.
imgflip.com/i/3idgag But, if you're going from a serious topic to a frivolous one, then it's a whataboutism.