What are Cookies?

According to DLC Websites:
Cookies are small files which are stored on a user’s computer. They are designed to hold a modest amount of data specific to a particular client and website, and can be accessed either by the web server or the client computer. This allows the server to deliver a page tailored to a particular user, or the page itself can contain some script which is aware of the data in the cookie and so is able to carry information from one visit to the website (or related site) to the next.
Each cookie is effectively a small lookup table containing pairs of (key, data) values – for example (firstname, John) (lastname, Smith). Once the cookie has been read by the code on the server or client computer, the data can be retrieved and used to customise the web page appropriately.
How Secure are Cookies? There is a lot of concern about privacy and security on the internet. Cookies do not in themselves present a threat to privacy, since they can only be used to store information that the user has volunteered or that the web server already has. Whilst it is possible that this information could be made available to specific third party websites, this is no worse than storing it in a central database. If you are concerned that the information you provide to a webserver will not be treated as confidential then you should question whether you actually need to provide that information at all.
More from this website on:
Are Cookies Enabled in my Browser?
Can I see/view the cookies I have on my computer?
What’s in a Cookie? When are Cookies Created?
Why are Cookies Used?
How Long Does a Cookie Last?
Who Can Access Cookies?
What are Tracking Cookies?
Visit its Computer Cookies Explained website http://www.whatarecookies.com/