Cookies are small text files a website stores on a visitor's device to recognize them on a later visit and remember things like login state, language preference, or items left in a cart. A site that offers to remember a username and password is using a cookie to skip that step on the next visit.
Not all cookies serve the same purpose. First-party cookies are set by the site itself and usually handle sessions and preferences; third-party cookies are set by other domains, most often ad and tracking networks, to follow a visitor's activity across multiple sites. That distinction is why cookies have become a privacy and regulatory flashpoint: GDPR, KVKK, and similar rules require sites to disclose what they're collecting and get consent, particularly for tracking cookies, which has pushed browsers to phase out third-party cookie support and pushed analytics tools toward cookieless measurement methods that rely on aggregated or first-party data instead.
