These are solar MC-4 connectors the FEMALE on the bottom and the MALE plug on top.. Today more and more solar panels are shipping with MC-4 terminals and less and less with actual junction boxes. I still personally prefer a water tight j-box, and water tight gland nut, but not all panels ship that way.
The MC-4 solar connectors are UL rated for 600V and up to 30A of current they are also IP68 rated which means they are fully "dust tight" and can be submersed to 1 meter and still retain water resistance.
They work well but on boats but if not carefully installed they can be a tad bulky and prone to being caught on things. That said, they are one of the better water tight electrical connections available for marine use. You don't have to use them only on solar connections and they could certainly be used for other applications.
Like any other project on boats this project will add yet another tool to your tool box.