Oh, thank you. I was desperately trying to work out if this was a "A16Z" (Andreessen Horowitz) thing...

I spent 15 minutes trying to figure this out the last time they popped up on HN. It's surprising to me how difficult this was to find out. I think it was buried in a FAQ somewhere.

I thought it was an 18-year-old female and wondered why that was considered worthy of a headline.

The thing you're referring to is called a "numeronym."

Lovely word. Thank you very much.

I always assumed it had some military symbolism. In the Army, all of the Special Forces jobs are 18 series (18A, 18B...).