Based on your analysis of the material we have studied this semester (i.e., the French Revolution, Haitian Revolution, American Revolution, Enlightenment, Renaissance, and Scientific Revolution), what is a revolution?

This is a very broad question, and you have different types of revolutions. In the French, Haitian, and American Revolutions, a revolution involved a government being overthrown and replaced with another. The change was quite rapid and bloody. In the end, the results of the political revolutions varied. The French overthrew their king and ultimately ended up with an authoritarian leader. The Haitian Revolution overthrew the French leadership of the island, but Haiti has not been prosperous since. The American Revolution may have ended the best possible way, with the people achieving a government that would be more responsive than the British parliament.
The Enlightenment and Renaissance were more gradual revolutions, and they were much more intellectual than political, though they had some political implications. People did not acknowledge these revolutions as they were taking place; rather, historians called them revolutions much later. These revolutions relied more on printed works and thinkers than political leaders and generals. Further, they were more widespread: the Renaissance ultimately affected all of Europe. The Scientific Revolution was experienced in the West and in the Middle East, as Arabic scientists contributed in terms of algebra, astronomy, and medicine.
A revolution is a time of change. One can look at events and mindsets before it and see radical change in people's lives after the revolution. You can discuss the differences between political and intellectual revolution as I have done here. You should also consider how intellectual revolutions (such as Enlightenment thought) affected political revolutions (such as the American Revolution). The term "revolution" is too broad to be summarized in one or two sentences.