When you ask the question, what is rum, it calls for a bigger question what is liquor. Liquor goes by many names hooch, booze, spirits, hard liquor, liqueur, and more.
Liquor is drinkable alcohol produced by distillation. It has a higher alcohol content than fermentation can naturally produce. Liquor can come from a variety of starches and can have flavoring added. Traditionally liquor refers to the common neutral spirits vodka, gin, rum, tequila, brandy and whiskey. A liqueur or cordial refers to neutral liquor that has added flavoring.
Rum is liquor derived from fermented sugarcane products often molasses. Rum has two main classes. Light bodied or white which is briefly aged and drier in flavor. Full bodied or dark Rum has added caramel and is aged in barrels yielding a rich brown color has a richer and fuller body in flavor.
So now you know what is rum, use this knowledge at your next party and sound smarter.