Your best friend Facebook (a.k.a. Facey B) knows more about you than even you do.
Do you ever scroll through your news feed and find very niche adds that are completely targeted to your bizarre interests?
Well, it's because every Google search, every Facebook like, and every Facebook page you visit informs Facebook what you are into, effectively building up a profile of your interests from which they can begin to target advertise.
From a business standpoint, you can't blame the smart guys and girls at Facebook as they are trying to sculpt an experience that is most fitting to you as an individual user.
If you're interested in what you are being targeted for, there is an easy way to find this out. If you go to Settings => Adverts => Edit, you can see and edit all of the areas of interest that Facebook has built up, examining your Internet history.
Below is an example from the Telegraph that lists all of the specific areas of interest in the 'TECHNOLOGY' category. It includes target words such as 'Mobile phones', 'podcast' and 'iPod Touch'.
As a Facebook user, you are free to tweak and delete any of these categories (for example, if you notice something you are not interested in). Editing these categories will have an impact on the kinds of ads that you will see in your feed.