You know what it is to "LIKE" something on Facebook, don't you?
It means you like a product, or a company and you are interested in what they are doing or have to offer. It means you are actually interested. So when a company has a new product info or event you get notified by it in your news feed. It is a little blip that goes by on you news feed about a product or service you LIKE. And if you decide you don't like that product or service you just unlike it. This is advertising tailored to suit your tastes or needs over time and it is non intrusive because YOU CHOOSE WHAT YOU LIKE. It is passive because unlike google you dont have to be thinking of it at that moment and perform a direct search. As the things you like change or grow you change what you like. Now I am always up to date with things I am interested in and would most likely purchase. My girlfriend uses this to keep up with clothes and fashion trends, as well as what all her friends are into. I do the same in a similar respect, music, photography and books, as well as restaurants and vacation locations. I also like to see what my friends are discovering and like as well.