The term "hardwood" refers to any wood taken from an angiosperm tree, as opposed to a coniferous tree. "Angiosperm" denotes any tree that reproduces via seeds while "conifer" denotes species that reproduce via cones. Hardwood comes from numerous species of trees, including maple, oak, sycamore, acacia, birch, ash, mahogany, beech, elm and willow. These trees produce hardwood by definition although in reality their wood is not always hard -- soft hardwood and hard hardwood both exist. A hardwood floor includes any flood made from a hardwood.
The term “sanded floor” describes any floor that undergoes the process of sanding. This process entails using a sanding machine or sandpaper to remove the top layer from a floor. Sanded floors are usually wood floors although technically speaking you can sand just about any surface. Sanding wood floors removes any dirt, grit and loose material on the surface of the wood, as well as scratches and stains. Properly sanding floors creates a level surface that always stays smooth. The process also highlights the natural grain patterns in wood floors.
The fundamental difference between hardwood floors and sanded floors lies in what these terms describe. “Hardwood floor” describes a specific type of floor, one made from a wood taken from a certain type of tree. The term “sanded floor” refers to any type of floor that undergoes a process. These terms do not necessarily describe different types of floors.
"Hardwood floor" and "sanded floor" are not mutually exclusive terms. Any floor that you sand, including a hardwood floor, constitutes a sanded floor. However, "sanded floor" may also refer to a material such as granite, on which you use a sanding machine to get a certain type of finish. "Hardwood," on the other hand, only refers to floors made from hardwood lumber. Even a floor made from a very hard coniferous tree does not count as a hardwood floor.