Solid hardwood is, as it sounds, wood through a plank. The fibers lie in one direction, parallel.
Engineered hardwood consists of one solid slice at the top with, underneath, with at least three layers of wood and other materials. (Note: The more layers, the better, because thickness matters here. It affects both durability and the number of times it can be sanded and refinished.)
Each layer is placed in a crosswise position, which makes the fibers crisscross.
While both have similarities, such as the ability to be sanded and refinishing and value-adding, both do have differences in functionality.
Since engineered can handle water and moisture better, there is more versatility as to the area in which it can be installed; for example, it shouldn’t be installed in a full bathroom where there’s heavy moisture, but installation in the half-bath is fine.
It also doesn’t shrink and expand to adjust to the weather, so no acclimation is needed.