MCL 206.4 — "Business income” defined

"Business income" means all income arising from transactions, activities, and sources in the regular course of the taxpayer's trade or business and includes the following:
(a) All income from tangible and intangible property if the acquisition, rental, management, or disposition of the property constitutes integral parts of the taxpayer's regular trade or business operations.
(b) Gains or losses from stock and securities of any foreign or domestic corporation and dividend and interest income.
(c) Income derived from isolated sales, leases, assignment, licenses, divisions, or other infrequently occurring dispositions, transfers, or transactions involving property if the property is or was used in the taxpayer's trade or business operation.
(d) Income derived from the sale of a business.