Commercial auto insurance covers vehicles a business owns, leases, or uses for work. It matters because a personal auto policy generally excludes regular business use, so a vehicle used for the business usually needs a commercial policy to be covered in a crash.
It can cover owned vehicles plus hired and non-owned autos (rented vehicles, or an employee's own car used for work errands), with liability and optional physical-damage coverage.
Example: a bakery buys a delivery van. A personal policy would deny a crash claim because the van is used for business, so the bakery carries commercial auto on it.
Related: hired and non-owned auto, liability coverage. See the commercial auto insurance overview.