AJAX is shorthand for "Asynchronous JavaScript and XML". Ajax is not a
technology in itself, but a term that refers to the use of a group of
technologies.
Although it is labeled as asyncronous in the term AJAX, that is not the only
way it can be used, it can also be used in a syncronous method. Syncronous is
useful if you need to have fully loaded the URL before the script continues,
asyncronous is useful if the next lines are not dependant on the XML and you
also would like to ensure that the browser does not lock up or loose
functionality while the script is executing in the background.
An XMLHTTP request has the capability to completely stall any script
activity.