And it never was.

In the original article about Ajax, the author states:

The name is shorthand for Asynchronous JavaScript + XML, and it represents a fundamental shift in what's possible on the Web.

Although he never calls it an acronym and never uses it as such, this particular statement can be blamed for the widespread misconception that Ajax is an acronym. Microsoft even thinks it's written as AJAX. Thankfully, most books get it right.

In my talk Tuesday night at New York PHP, I tried to provide a concise and precise definition of Ajax as I interpret it:

Client-side technologies / techniques that allow two-way communication between the client and the server.

I want to include all of the creative client-side techniques used to communicate with the server (e.g., IFrames) without including the purely client-side techniques that don't interact with the server and therefore aren't Ajax at all.

I think my simplistic definition might still be too restrictive, though. In the case of something like Netflix's star rating, the goal is just to send the rating to the server. You can update the interface with CSS, so two-way communication isn't necessary. You could argue that the use of <script src=""> doesn't really constitute two-way communication either. I'm sure there are other examples.

How do you define Ajax?