Simply put, a hypercane is a hurricane from hell.
It's not the scientific terminology, but it's close. A hypercane is a hypothetical super-mega-hurricane.
So far we have no hypercanes on record in human history, although according to Kerry Emanuel of MIT, the researcher who developed this hypothetical model and named it, a series of them may have landed the dinosaurs in hot water, shortly after that famed asteroid dropped out of the sky.
To create a perspective of what a hypercane would look like, here is a size comparison of the largest typhoon on record, the 1979 super typhoon Tip, and one of the largest hurricanes in human history, the 1974 super hurricane Tracy.
A hypercane could easily be double the size of typhoon Tip.
However, the only way such a hurricane could form would be through an extremely heated ocean, such as through an asteroid impact or a volcanic eruption. The ocean would have to be heated to at least 50 °C (or 122 °F) in order to form. Winds would exceed 800km per hour (500mph), strong enough to rip most things off the ground.
Such a mega-hurricane would have the power to scratch up the earth's ozone layer and effectively damage the entire planet.
While for now such a hypercane is only a theoretical and hypothetical scenario, it is still a possibility. Especially if an asteroid or meteoroid decides to drop in anytime soon.