Going through this old blog post (15 years ago!)
Ironically, Microsoft unintentionally helped create Ajax. The x in Ajax is from the XMLHttpRequest object, which lets the browser communicate with the server in the background while displaying a page. (Originally the only way to communicate with the server was to ask for a new page.) XMLHttpRequest was created by Microsoft in the late 90s because they needed it for Outlook. What they didn’t realize was that it would be useful to a lot of other people too—in fact, to anyone who wanted to make web apps work like desktop ones.