Like-kind property is real property held for investment or business use. Nearly any U.S. investment real estate is like-kind to any other.
Since the 2017 tax law took effect in 2018, 1031 treatment applies only to real property, not equipment or other personal property. The word like-kind refers to the nature of the property, not its quality or type, so an investor can often exchange a duplex for a NNN retail building, for instance. The property must be held for investment or business use, and not primarily for resale. A residence or inventory generally does not qualify.