Mich. Comp. Laws § 257.5: "Business district" and "commercial business" defined.

Sec. 5.

(1) "Business district" means an area contiguous to a highway where the total widths of the adjacent buildings in use for commercial business open to the general public on both sides occupy 50% or more of the total frontage on both sides for a distance of 600 feet or more.

(2) As used in this section, "commercial business" does not include a home-based business conducted from a residence or domicile, but does include a multi-use building in which a commercial business open to the general public is operated on the ground floor and residential apartments exist on upper floors.