UL refers to the type of plug the pump has. If the pump has a designation UL it means that there is a 3rd prong grounded cord. Without it means it is a standard 2 prong cord.
It is highly recommended that if you you use these pump for outdoor use that you use the pumps that have a UL listing beside them.
A 2 prong plug should only be used if there is not chance the outlet can get wet.