On History: Oh no, "revisionist history!"
Folks, history is supposed to be revised!
It is through revision, specifically -- through being looked at by hundreds or thousands or millions of people, not just one, through being reexamined when new evidence is brought to light, through being interpreted by the lenses of many readers, not few -- that we have any hope of ever getting to the truth of any historical event.
Any time the popular belief on a subject gets the ol' pillars shaken by a new historical argument, revisionist history is taking place. As long as that pillar shaking is true, and can be verified through well documented sources? It's absolutely a good thing, not a bad one!
Since the current topic of virulent debate (surprise, it's Glocktalk!) is the Civil War, let's go with the Battle of Gettysburg, shall we? Imagine you could only read one thing, ever, written about the battle -- quick! -- would you pick one written the day after Gettysburg, or the day before yesterday?
If it was written shortly after Gettysburg, I assure you they didn't have time to properly research anything, gather orders from every officer and interview soldiers to find out what they saw (or what they thought they saw), filter through all that to see what made sense, collect casualty reports, assess the strength of remaining troops, understand the motivation of the Generals making the decisions, and to try and put together a comprehensive picture of what actually happened. The headlines said "thousands killed and wounded at Gettysburg" because they really didn't know how many thousands, for instance.
If you picked one written much more recently, well, guess what? You're an advocate of the dreaded revisionist history.
Anything at all written about the Battle of Gettysburg that deviates from the very first newspaper article written -- every official Union or Confederate casualty or prisoner report to come days or weeks later, for instance -- has been revisionist history. Why? Because that's how you make history better. You add to what's already there, you read correspondences and memoirs written by men who were there, you dig up and find official unit enrollment records to more accurately gauge the strengths of both sides, you add to the canon by finding files full of medical records previously thought lost, you share new resources or a new interpretation of old ones, you use new technology (battlefield re-creations with a mixture of computer ballistic simulations and real world tours of a site are amazing), you collect existing sources and see something someone else missed...that's how the work gets done. That's how the truth gets uncovered, and revised, and revised again, and revised again, until -- maybe -- we actually get it right.
Opinions change. Interpretations change. Details change. History changes.
You can't trust just a single source, ever. Hell, the Wikipedia page for the Battle of Gettysburg lists thirty six difference sources, and that's just Wikipedia! You wouldn't get 142,000,000 hits on Google for "Battle of Gettysburg" if any one source -- written at any one time! -- could tell you everything there was to know, would you? Well, any time one of those 142,000,000 disagrees with one of the 141,999,999 other hits, someone's writing revisionist history.
Historical revisionism is a completely legitimate scholarly process, where the historical record is changed because new information is available. It shouldn't be used as a curse or an insult, or as a way to try and dismiss or belittle an argument you disagree with.
The term you're looking for in this sort of instance is negationism, even if Firefox's built in spellchecker tries to tell you it's not a word. Negationism is a hallmark of amateur historians who purposefully distort the past in order to twist it to suit their own -- often political -- ends.
Holocaust deniers are among the most infamous advocates of negationism, as are apologists for Socialist and Communist totalitarian regimes, or folks who'll claim stuff like the whole Rape of Nanking never happened. Politicians do it pretty much every time they open their mouths and talk about a past term in office, like Hillary Clinton's nonsense about personally dodging sniper fire all those years ago. Speaking of the Holocaust and politicians, in fact, Hitler himself used negationism when he whipped the German people into a frenzy and seized power, clinging to certain aspects of the Treaty of Versailles and blowing them out of proportion, exaggerating the financial problems the people of Germany had at the time, and twisting the truth in order to blame those problems on convenient scapegoats (and we all know how that ended).
Negationism is bad. It's sloppy history, and normally it's sloppy history on purpose. "Articles" that use negationism won't be peer reviewed, or their footnotes won't check out (if you bother to check them, and you do check the footnotes before you really believe something, right?), or they'll claim to be sharing "the real truth" or "secrets" or something else that they then won't have any way to verify.
Not all historical revision is negationism, though. Most of it, in fact, isn't!
The government mandated rewriting of China's history (in blood) in order to diminish the contributions of every other nation on Earth, in order to glorify the Communist regime, in order to conveniently ignore the millions upon millions upon millions of people who lost their lives during The Great Leap Forward? That's despicable negationism of the absolute worst sort.
The string of legitimate historians -- Bannister, Chang, Jones, Dikotter, Halliday, Jisheng, Rummel, Yang -- that came along afterward, and tried to gather and present enough evidence to share a compelling argument, and tell the world about the horrors Mao had wrought?
Those guys and gals were revisionist historians, and God bless 'em for it.
So do me a favor, folks. Don't spit out the words "revisionist history" next time someone says something you don't like, about a historical event you feel strongly about. Call it negationism, if you really think they're purposefully twisting or distorting the truth, ignoring aspects of what happened, or something similar.