The best example you can understand facebook target audiences :
There are 4 types of targeting audience it is a simple way you can understand.
 Unknown Audience
In this type audience, you can not know which type of audience e.g
- Age / Gender
- Education Details
- Job Details
- Company Name
 known Audience
In this type of audience, you can know user information e.g
- Phone Number
- Website Visitor
In this information you can know so directly you can use this information for Remarketing.
 look like Audience
In this type of Audience is a way to increase reach new people who are likely to be similarly interested in your business.
 Friends of Friends Audience
In this type of audience show Ad your All your facebook friends list.