Lookalike audiences are used in Facebook advertising. They are an audience that you create from a source audience, such as website visitors or a customer list that you have uploaded into the back of your Ads Manager.
Targeted audiences are a great way to get really specific with your online advertising. The first thing you are going to want to review is your Ideal Customer Avatar. This is your idea (for lack of a better word) of what your prospective online customer looks like.