A Dark Pattern is a user interface that has been carefully crafted to trick users into doing things, such as buying insurance with their purchase or signing up for recurring bills.
Normally when you think of “bad design”, you think of the creator as being sloppy or lazy but with no ill intent. This type of bad design is known as a “UI anti-pattern”. Dark Patterns are different – they are not mistakes, they are carefully crafted with a solid understanding of human psychology, and they do not have the user’s interests in mind. We as designers, founders, UX & UI professionals and creators need to take a stance against Dark Patterns. — Source