As the name implies, this type of wood flooring is solid wood all the way through, from top to bottom. It's similar to any other stick of lumber that is taken straight off the log - no additional materials are added. It's usually just called "hardwood floor."
Hardwood flooring comes either unfinished or prefinished. Unfinished hardwood tends to be a little cheaper than prefinished, but does require immediate light sanding, staining (optional), and sealing after installation. With prefinished, you can walk on it right after installation. With unfinished, you need to limit usage until it has been sealed. After sealing, you will need to wait at least 48 hours for the sealant to dry. Even then, additional coats may be required. With unfinished, the advantage is you can stain it and seal it to your exact specification. With prefinished, the advantage is the quick turnaround time. Hardwood flooring's greatest advantage is that it can be re-sanded numerous times, extending its life literally for decades.
Engineered wood flooring is an alternative to solid hardwood flooring. Engineered flooring basically is a sandwich of finished wood and plywood. The finished wood is what you see and walk on. The plywood underneath comprises 80-90% of the floor.
It is the plywood that distinguishes engineered wood flooring from solid hardwood. Each ply runs perpendicular to its adjacent ply, giving dimensional strength to the sandwich. This means that engineered wood flooring stands up well to areas with light moisture--basements and bathrooms.
Laminate flooring is not real wood, at least not in the way that hardwood and engineered wood are. It is comprised of a thin top layer of resin-infused paper on top of a wood-chip composite.
Laminate flooring is an assimilation of wood. The resin layer is essentially a photograph of wood. Laminate flooring can be hard to walk on (foam under layer is put down to soften this), it is slippery, and it cannot be sanded.
Site finished floors have many benefits. For example, the boards fit together more tightly, and you can customize the colors. The disadvantages are that once the floor is put in, it has to be sanded, stained and coats of finish applied.
For the pre-finished floors, the benefit is that once they are put down, the are finished. No additional work required! The disadvantages are you cannot customize the color, and the boards are beveled.