One owner, multiple companies - single or multiple employer plan?

[TPApril]

One owner has 4 separate businesses, all somewhat related, working at the same location, but separate employees.  single or multiple employer plan? I'm thinking Single.

[C. B. Zeller]

What does "somewhat" related mean?

Are all four businesses owned 100% by the same person? Then they are all part of the same controlled group.

Did all four businesses in the controlled group adopt the same plan? If there are no other adopting employers outside the controlled group, it is a single employer plan.