That doesn't mean I'm not going to not not explain it to you.
Much like the previous sentence, this product needs no explanation. Some of us still remember the good ol days where BNC was King of the connections and only the absolute best monitors (CRT screen and all) had them. BNC (Bayonet Neill–Concelman, named after it's inventors) was originally designed for the military but quickly became a favourite in broadcast radio and television due to its superior connection and minimal wave reflection/loss. It was even used to transfer data on some of the earliest computer networks such as ARCnet and the IBM PC Network.
This fine example of an adapter features a Male RCA connector and a Female BNC connector.
Fun Fact: Sometimes, incorrectly, the acronym for BNC is referred to as coming from "Berkeley Nucleonics Corporation"