A cookie is a small text file that a website stores in your browser. It works like a loyalty card at a store - when you show the card, the store recognizes you as a returning customer. Similarly, when your browser sends a cookie back to a website, the site knows who you are and can remember your preferences.
Cookies serve three primary purposes. First, they maintain login sessions. When you log into a social media site or email service, a cookie keeps you signed in as you navigate between pages. Without cookies, you would need to enter your password on every single page. Second, cookies preserve shopping cart contents. When you add items to a cart on an online store and continue browsing, the cookie remembers what you selected. Third, cookies store site preferences such as language settings, dark mode choices, and display options.
Privacy concerns around cookies have grown significantly. Third-party cookies allow advertising companies to track your browsing activity across multiple websites, building a profile of your interests to serve targeted ads. Regulations like the EU's GDPR and Japan's amended Act on the Protection of Personal Information now require websites to obtain user consent before setting non-essential cookies. This is why you see cookie consent banners on many websites.
URL shortening services use cookies for click analytics. When measuring unique visitors, cookies help distinguish between one person clicking a link ten times and ten different people each clicking once. Without cookies, accurate visitor counting becomes much more difficult.
Technically, each cookie is limited to about 4KB in size, and a single website can store up to approximately 50 cookies in your browser. Cookies have expiration dates - session cookies disappear when you close the browser, while persistent cookies remain until their set expiration date or until you manually delete them. You can view and delete cookies through your browser's settings. You can find related books on Amazon.