That means this person is covered by an Employer plan.

"The partner cannot deduct the premiums for any calendar month, or part of a month, in which the partner is eligible to participate in any subsidized health plan maintained by any employer of the partner, the partner’s spouse, the partner’s dependents, or any children under age 27 who are not dependents. For more information on the self-employed health insurance deduction, see chapter 6 in Publication 535."

https://kb.drakesoftware.com/Site/Browse/10109/1065-Entering-Payments-for-Partner-Health-Insurance

There typically is a qualification for "who" establishes the plan, if the premiums are paid pre-tax, reimbursed, paid directly by the entity, etc.

Every difference matters.