Simply put, a solid wood floor is made from one solid piece of its wood e.g. oak. There are variations of this where a plank is made up of pieces of solid wood to give a strip effect floor.

An engineered wood floor is made up of layers. There is the top Layer, which is the veneer or wear layer as we call it. This is what is visible from the top and once laid. Beneath this is usually plywood that is manufactured from thin layers of wood that is glued together with each adjacent layer having their wood grain rotated up to 90 degrees to one another (cross-laminated). This is done to give the floor much more stability in the floor with changes in climate as opposed to solid wood flooring.