Besides being a delicious treat, cookies are a special kind of small computer file that helps a website recognize repeat visitors.
Originally, when the internet was first invented, a website had no way of distinguishing regular users versus first-time visitors. Instead, everyone was treated as though it was their first time visiting the website. The solution to this problem was the invention of cookies.
For WordPress, however, there are only two kinds of cookies, known as session cookies and comments cookies.
Session cookies are the simplest kind and work to recognize a registered WordPress user and make sure they remain logged in. WordPress session cookies expire every 15 days, but will be automatically renewed every time you visit a WordPress site (unless cookies are disabled).
Comments cookies are a little more sophisticated. Every time a user leaves a comment on a WordPress website, a cookie is generated with the user’s name, email address, and other information. Since spam is a big problem with comments on WordPress, the comments cookies help a WordPress site recognize an authentic user who has written a comment. Comments cookies expire in around 347 days.
There are also WordPress plugins that generate cookies.