Are all Stallions male or can they be female as well?

I’m starting a new job as a Stable Hand with limited experience, and my new "boss" told me at the interview that stallions can be either male or female, and they have not been gelded.

I’ve been doing a bit of research, and every site I’ve been on tells me stallions can only be males, that are not fixed. Can somebody clear up this confusion please?

What kind of idiot is your boss? a stallion is an ungelded male – END OF DISCUSSION.