A cookie is a small amount of data generated by a website and saved by your web browser. Its purpose is to remember information about you, similar to a preference file created by a software application.
While cookies serve many functions, their most common purpose is to store login information for a specific site. Some sites will save both your username and password in a cookie, while others will only save your username. Whenever you check a box that says, "Remember me on this computer," the website will generate a login cookie once you successfully log in. Each time you revisit the website, you may only need to enter your password or you might not need to log in at all.
Browser cookies come in two different flavors: "session" and "persistent." Session cookies are temporary and are deleted when the browser is closed. These types of cookies are often used by e-commerce sites to store items placed in your shopping cart, and can serve many other purposes as well. Persistent cookies are designed to store data for an extended period of time. Each persistent cookie is created with an expiration date, which may be anywhere from a few days to several years in the future. Once the expiration date is reached, the cookie is automatically deleted. Persistent cookies are what allow websites to "remember you" for two weeks, one month, or any other amount of time.
Most web browsers save all cookies in a single file. This file is located in a different directory for each browser and is not meant to be opened manually. Fortunately, most browsers allow you to view your cookies in the browser preferences, typically within the "Privacy" or "Security" tab. Some browsers allow you to delete specific cookies or even prevent cookies from being created. While disallowing cookies in your browser may provide a higher level of privacy, it is not recommended since many websites require cookies to function properly.
NOTE: Since cookies are stored in a different location for each web browser, if you switch browsers, new cookies will need to be created.