Cookies are small text files that are stored on a user's computer by a web browser when they visit a website. They are commonly used in web development for a variety of purposes, such as user authentication, personalization, and tracking.
Cookies can also be used to track user behavior on a website, such as which pages they visit and how long they stay on each page. This information can be used to improve the website's functionality and user experience.
However, cookies have been controversial because they can also be used to track user activity across multiple websites, which has raised privacy concerns. In response, many web browsers have implemented features to limit cookie usage, such as blocking third-party cookies by default.
In summary, cookies are a useful tool for web developers to provide a personalized and efficient browsing experience for users, but it's important to use them responsibly and with respect for users' privacy.