I don't know if this will be helpful, but a Fringe is typically a taxable benefit given instead of the money as money. When you mention retirement plans, and they are qualified plans, and they fall under ERISA, they are a completely different animal from a Fringe, even though these are benefits often used as a means of retention. Offering retirement plans as Defined Benefit has changed to Defined Contribution meaning, the employee participates actively. There are employer match, such as SIMPLE IRA is typically a 50% match up to the employee's own 6% limit of annual wages, which is why it is also typical to see "3% employer match." But there also is an optional, sort of voluntary, one lump amount from the employer without participating contribution by the employee, a sort of Profit share or Bonus that would be 2%, for instance.
The specifics of the plan, the agreement for the employee, etc, really matter for determining what things really are. I've helped lots of people figure out they had the pre- vs post-tax settings wrong for the payroll functions, or adding Fringe benefit as not taxable (which, agreeably, a few are not taxable, such as per diem).
You have asked a few questions, but this relates to a matrix of "what is this thing?"
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