When we have no idea what the possible range of outcomes are, that is when we can describe something as uncertain. War is often a good example of this; consider the uncertain prospect of the invasion of Iraq in 2003 leading to the rise of Islamic State in 2014.
We often hear the phrase “uncertainty” used when people are uncomfortable admitting a lack of ability to foresee the future; anecdotally, this seems to be especially true when they have been recently wrong.
Which brings us to the presidential race and the uncertainty trope.
Just about all of the pundits were wrong about the Republican primary race; similarly, the Democratic race was supposed to be over long ago. The establishment of one party and the more enthusiastic activist base of the other are unhappy with the presumptive nominees. That combination of “wrongness” and dissatisfaction has once again led to the misuse of that word again.
The outcome of the U.S. 2016 presidential race is anything but uncertain: It's either going to be either Donald Trump or Hillary Clinton (that one in a million chance of Bernie Sanders is rapidly fading). The two frontrunners have been on the stump for a long time. Both are very well-known quantities. To say that the outcome is uncertain is to misunderstand what that word means.
You may not love the choice of candidates. You may not be happy with their policy positions. Maybe you're even toying with leaving the country if one or the other of the candidates wins. But this much is certain: it's only the outcome of the election that is unknown today. But that is something very different from “uncertain.”
Almost every time I see “uncertainty” in print, I am reminded of the movie "The Princess Bride," when Inigo Montoya says “You keep using that word. I do not think it means what you think it means.”
Keep that in mind the next time someone tells you that uncertainty accounts for something unpleasant in markets or the economy.