Mich. Comp. Laws § 418.601: Definitions.

Sec. 601.

Whenever used in this act:

"Insurer" means an organization that transacts the business of worker's compensation insurance within this state.

"Self-insurer" means either of the following:

An individual employer authorized to carry its own risk.

A group of employers who pool their liabilities under this act as a group fund in the manner provided in section 611.

"Carrier" means a self-insurer or an insurer.