It's common to use the word "them" to talk about one person, when you don't know the person's gender:

A: This morning someone asked if you and I were dating.

B: What did you tell them?

Using "them" to talk about just one person isn't technically correct English. Technically, you should say something like "him or her" instead. But "them" is much more common in casual English.

This phrase appears in these lessons: