Cookies are little files or other pieces of data that websites store on a user's computer. Cookies are useful and can be used in both, beneficial and malign ways. By identifying the user, they can help store information such as user preferences, login information, and shopping cart contents. But they can also track users and their browsing activity across the whole web, enabling their operators to collect a multitude of data and aggregate them into profiles to target specific content to specific users. All that is, of course, a kind of data processing. Therefore, consent is required.
That Cookie Consent is a mechanism of informing the user of a website about the cookies used on the site and obtaining permission to store them in the user's browser. This helps ensure that the user understands what data is being collected, why it's being collected, and how it will be used.
Typically, the tool used is a banner with information and choices the user can make. The user's choice must be free, and they must not be nudged into blindly accepting unwanted cookies, thus the use of so-called "dark patterns" is forbidden, such as pre-ticked boxes or making it easier to accept than to reject cook-ies.