The classic tropical spirit, rum is made from either sugarcane or a byproduct like molassas. It can be either aged in oak barrels or bottled as-is. Most of the light, unaged rums are designed for use in cocktails while the aged rums offer a complexity and depth of flavor that is best suited for drinking straight or on the rocks.
Looking into the rums, you'll notice different styles pretty easily. The youngest and usually lightest are often called "silver" or "white." These rums are either unaged or have been treated to remove color obtained after aging. They generally are your lighter, cleaner rums and are best suited for cocktails. After those are the "gold" rums—they typically get their color from either barrel aging or added coloring. The next grade to watch for is the "dark" rums, distilled from carmelized sugar or molassas and barrel aged. These rums pack the darkest flavor and offer the most wood-tone of the rums. These rums harken towards the tannic traits of well-aged whiskeys and bring a bit of dryness to rums that is not prevalent in other styles.
Perhaps the most familar are the spiced rums, which are traditionally based on gold rums and flavored with spices like cinnamon, aniseed, cardamom, and rosemary among others. These rums are great for Cuba Libres or simple rum-and-cokes and are called for in countless other cocktails.