According to Facebook terms, you can target those people on Facebook for ads. What you can’t do is use data you’ve learned about those people via Facebook ads for other promotions.

For example, if someone fills out a form on your site that says “I am a woman in San Francisco”, you can use that information however you like.

Now, let’s say you are targeting “women in San Francisco” as a Facebook audience, save in your database the user IDs of people who came from a “women in San Francisco” ad and then use that data to build a promotion. In this case, you’re violating the privacy of those people who have not explicitly told you information about them. This is against the Facebook terms.