Ajax allows content on Web pages to update immediately when a user performs an action, unlike an HTTP request, during which users must wait for a whole new page to load. For example, a weather forecasting site could display local conditions on one side of the page without delay after a user types in a zip code.
Google Maps is one well-known application that uses Ajax. The interface allows the user to change views and manipulate the map in real time. Ajax applications do not require installation of a plug-in, but work directly with a Web browser. Because of the technique's reliance on XMLHttpRequest, early applications worked only with Microsoft's Internet Explorer browser, but most other browsers now support Ajax.
Editors at our sister site, The Ajaxian, blog about Ajax news and trends.