AJAX (web technology)/Definition

Ajax is Javascript in a web page, making HTTP GET or POST requests, and providing a callback function which gets called back by the web server 4 times. Upon the fourth callback, the response is ready for processing, and at that point, the Javascript callback function parses the answer out of the string sent back from the web server and then updates some part of the web page with the new information. While this is happening, the web page is available for the user to use and interact with; the user only sees the result of the Ajax call and is not blocked from scrolling around the web page and interacting with it while the call is in progress in the background.