HyperText Transfer Protocol
From Unofficial BOINC Wiki
The Protocol that is used on the Internet to allow the transmission of data between a Web Server and a Web Browser. This Protocol is stateless which means that each communication between the Web Browser and the Web Server is independent of any other previous communication. Most of the impact of this is on the Web Server side of the equation because, for example, if you are shopping and putting items into your "cart"; the next time that you make a selection the Web Server has to be told what other items might be in the cart because it maintains none of information established in the past.
This is one of the reasons for the "cookies" that may be maintained on your system (there are other ways of doing this, the use of "cookies" is only one of the ways it is done). All of the information that is needed by the Web Server will be maintained within the cookies created on your computer. So, the cookie becomes the "repository" of all of the state information that the Server might need to appear intelligent and complete session. Other mechanisms include using Java or other programming language to enable a transfer of information that does maintain state information for the compete session. The Web Server could also keep this information in a database as part of an account with the site, so the repository is kept server-side.