The first use of the term in public was by Jesse James Garrett in February 2005. Garrett thought of the term when he realized the need for a shorthand term to represent the suite of technologies he was proposing to a client.
Although the term Ajax was coined in 2005, most of the technologies that enable Ajax started a decade earlier with Microsoft's initiatives in developing Remote Scripting. Techniques for the asynchronous loading of content on an existing Web page without requiring a full reload date back as far as the IFRAME element type (introduced in Internet Explorer 3 in 1996) and the LAYER element type (introduced in Netscape 4 in 1997, abandoned during early development of Mozilla). Both element types had a src attribute that could take any external URL, and by loading a page containing JavaScript that manipulated the parent page, Ajax-like effects could be attained. This set of client-side technologies was usually grouped together under the generic term of DHTML. Macromedia's Flash could also, from version 4, load XML and CSV files from a remote server without requiring a browser being refreshed.
Source: Wikipedia.org
