There are other instances but much less likely where you would see that. It could be an estate that is subject to a license to sell. Most likely, it is a short sale. They are very prevalent in today's market place.
This typically means that the asking price is a "short sale" meaning, the asking price is less than is owed on the property. The short sale process can be a bit tricky, and the time frame is usually quite a bit longer than a "traditional" transaction.
In this day and age it most likely means your dealing with a short sale, which means after an Offer is made the bank has to approve the Offer. Or it means that there is another person besides the seller involved in the transaction ie. an estate, where the family makes the decision or the attorney involved.
Third party is any person besides the seller who makes the decisions.
Hope this helps.