What does it mean for the web and the HTTP protocol to be stateless? Why are they stateless?
Stateless meaning:
It does not keep track of configuration settings, transaction information or any other data for the next session. When a program "does not maintain state" (is stateless) or when the infrastructure of a system prevents a program from maintaining state, it cannot take information about the last session into the next, such as settings the user chose or conditions that arose during processing.
HTTP:
The HTTP protocol, which is the communications vehicle for Web transactions, is stateless. After a Web page is delivered to the user, the connection is closed. Counter measures, such as the use of cookies, have been developed to maintain the state of a user moving from page to page on a Web site.
OR it can be simple web definition:
A protocol is stateless if there is no relation between subsequent request-response pairs. The server can handle each request uniquely and does not have to keep a session state for the client.