Solid Wood flooring comes in three basic types:
STRIP flooring accounts for the majority of installations. Strips usually 2-1/4 inches wide, but also come in widths ranging from 1-1/2 inches to 3-1/4 inches. They are installed by nailing to the subfloor.
PLANK flooring boards are at least 3 inches wide. They may be screwed to the subfloor as well as nailed. Screw holes can be covered with wooden plugs.
PARQUET flooring comes in standard patterns of 6 inches x 6 inches blocks. Specialty patterns may range up to 36 inches square units. Parquet often achieves dramatic geometric effects of special design patterns.
Solid wood floors can be installed on a concrete slab as long as the floor is on or above ground level. They can be sanded and refinished over several generations of use.

Solid wood flooring expands and contracts with changes in your home's relative humidity. Normally, installers compensate for this movement by leaving an expansion gap between the floor and the wall. Base moulding is the traditional (cover-up) for this gap.
Engineered wood
Made of several layers of different woods or different grades of same wood stacked and glued together under heat and pressure. Engineered wood flooring is less likely to be affected by changes in humidity and can be installed above, on, or below ground level. Some engineered wood floors with thicker top layers can be sanded up to three times. Some can't be sanded at all.
Wood laminates
A plywood base topped with a layer of veneer. Plies and thicknesses vary, but three-ply, 3/8 inch flooring is most common. (Remember that solid hardwood floors, at 3/4 inch, are twice as thick as wood laminates.) The veneer topping of wood laminate floors (commonly 1/8 inch thick) can be sanded and refinished (in rare cases, three times.) Most manufacturer warranties cover the finish for five years.