These are solar MC4 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 MC4 solar connectors are UL rated for 600V and up to 50A of maximum current. They also range from IP65 to IP68 rated (depends upon brand) which means they are fully "dust & water jet tight" (IP65) and can be submersed to 1 meter for 1 hour and still retain water resistance (IP68). The MC4 connectors are available in 14, 12, 10 & 8GA sizes.
14GA = 22.5A
12GA = 37A
10GA = 43A
8GA = 50A
They work quite 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.