It’s a DE9, not a DB9

You've seen them everywhere, especially on older computer equipment: the classic 9-pin serial connector. You probably know it as a DB9. It's an iconic connector for makers, engineers, and anyone who's ever used an RS232 serial device. Here's a little secret, though: calling it a DB9 is technically wrong. The correct name is actually DE9.

Christo-boots with the-pher at Sparkfun Electronics

I honestly had no idea, and looking through the Wikipedia page, it seems this isn't the only common misnomer when it comes to D-sub connectors.