Solid hardwood is real wood flooring. This means it's true wood throughout the entire product. That is why natural hardwood floors can be sanded/refinished multiple times. Real hardwood is known for being durable, timeless design and will add a lot of value to your home when it comes time to resell or rent.
Engineered hardwood floors are a composite of solid wood on top and bottom, but the core layers in the middle are made of plywood. The benefit of engineered hardwood is that they are less likely to expand and better suitable for installing over radiant heating systems, concrete slabs, and basements.
Solid hardwood is great for high-traffic spaces and rooms on the 1st or 2nd floor where there is less moisture. You can buy solid hardwood flooring either prefinished or unfinished. Prefinished hardwood floors have a coating that protects them. Prefinished wood flooring is ready for installation, directly out of the box. Unfinished hardwoods provide you the ability to customize your own unique stain/color.
Similar to solid hardwood floors, engineered hardwood flooring comes in a wide variety of styles, colors, and natural wood species. Engineered wood floors can also be sanded and refinished, just not many times as solid wood flooring because it's not entirely hardwood through and through.