Your ad preferences let you view, add and remove preferences Facebook has created for you based on things like your profile information, actions you take on Facebook and websites and apps you use off Facebook. For example, if your preferences include “cycling” you might see ads from a local bicycle shop. Changing your ad preferences influences which ads you see, but it won’t change the total number of ads you see. If you don’t want Facebook to use information based on your activity on websites or apps off Facebook to show you ads, you can opt out from your settings.
Learn more about how Facebook decides which ads to show you and how to give feedback on the ads you see.
Source : https://www.facebook.com/help/109378269482053?helpref=hc_global_nav