What is a cookie?

A cookie, sometimes called a web cookie, or a browser cookie, is a small piece of data sent from a website and stored on a user’s web browser while the user browses a website. A cookie is usually a string of text, numbers and some alpha-numeric characters stored as a text file on the users computer.

When a user re-visits the same website at a later date, the data stored in the cookie can be retrieved by the website and the user’s previous activity can be reviewed, their details retrieved or their browsing history referenced for this ‘new session’. We are most familiar with the use of cookies by membership or shopping sites where the user is welcomed with a customised message – like ‘Welcome back Susan’. In the case of a shopping site, the website may show the user shopping basket contents that they didn’t purchase or books they previously used.  Cookies can be either ‘session cookies’ which are valid for ‘browser session’ and are deleted when the user closes or quits the web browser.

A ‘persistent’ cookie can remain on the users computer after they quit the web browser or even shut down the computer. These cookies may have an expiration date set a long time in the future – effectively never expiring unless the user clears, or deletes, saved cookies from their web browser in the preferences panel.

Cookies perform essential functions for most web users, from authentication to search history. Cookies help website owners to ‘follow’ a users path through a transaction so the website is aware of what’s in your online shopping basket when you get to a check-out page, even though the transaction may be completed over a number of days Cookies also help advertisers to show advertisements relevant to items or sites a user may have searched for previously on the web.


  1. Javascript Cookies @ W3C – the basics
  2. SilkTide Cookie Consent script
  3. EU Directive on Privacy @ Wikipedia