Attitudinal targeting is when companies try to figure out how you feel about certain things, like a particular product or service, and then show you ads or promotional materials that are more likely to match your interests and feelings.
Imagine you really like cars and always look at car websites online, and you also love the color blue. A company might use attitudinal targeting to figure out that you are interested in cars and the color blue, and then show you ads for blue cars or car-related products.
It's like a teacher giving you easier or harder homework based on what they know about your abilities. Companies use attitudinal targeting to give you ads that are more likely to interest you, because they want you to buy their products or services.