The term Ajax is a set of standard techniques for creating dynamic pages, but it coexists with other techniques such as iframes and other technologies to exchange data with the server, and they are different things.
However, technologies that make up Ajax are evolving and thus it must evolve too.
Evolution of Ajax is in fact inevitable because Ajax is a combination of technologies that themselves are improved over times:
Ajax does not therefore designate something rigid, even if we stick to components originally described in the article by J. J. Garrett (see link below).
Finally, Ajax is replaced by a more powerful protocol, WebSocket, allowing interactions between client and server at the initiative of either party. However, the XHR object does not become obsolete and remains useful on dynamic pages whose changes depend only on the user.
Ajax, a new approach to web applications
The article that has coined the term Ajax and popularized its use.