Engineered hardwood is simply a pre-finished hardwood surface layer with either a plywood or high-pressure laminate core. The surface finish and quality is the same as solid pre-finished hardwood, and the plywood or laminate core technology makes engineered hardwoods far more resistance to expansion and contraction. Most engineered hardwood is between 3/8" thick and 5/8" thick, and comes in a wide range of lengths and widths.
Though most manufacturer's of pre-finished hardwood now recommend a simple plank replacement as the repair technique of choice, most engineered hardwoods can still be sanded and refinished one or two times. Generally, surface texture and elaborate factory finishes mean that refinishing the wood is a thing of the past - more appropriate for sand-in-place wood products.
One major advantage that engineered hardwood has over solid hardwood is the reduced acclimation time required before installation can begin. And the slightly shorter flooring height means easier transitions to other flooring in the house.