Contrary to popular belief, the difference between hardwood and softwood has little to do with the density of the wood itself. Instead, these designations refer to how the tree reproduces. A hardwood is an angiosperm (or flowering plant) that reproduces by dropping a hard seed, such as a fruit seed or an acorn. A softwood is a gymnosperm, which spreads its seeds more freely, typically producing cones that allow the wind to distribute the naked seeds far and wide.
Overall, hardwoods do tend to be more dense than softwoods, but there are exceptions -- such as feather-light balsa wood, which is classified as a hardwood.
What wood works best?: