In short; AJAX is about loading data in the background and display it on the webpage, without reloading the whole page.
Examples of applications using AJAX: Gmail, Google Maps, Youtube, and Facebook tabs.
JQuery aims to ease all these problems by providing a lightweight library that adds many advanced and cross-browser functions to the standard language. In addition, there is a very dynamic community that adds more-advanced components based on JQuery.
jQuery has a large set of library/functions.
jQuery has good documentation and help manuals are easily available.
jQuery supports AJAX functionality.
You are no longer writing the native language, so your understanding of what is actually occuring may be limited.
With Ajax in a website there is no need to refresh a Web page continuously. For users who are waiting to see if they won an auction, keeping an eye on sports scores, or closely following the latest weather forecasts, Ajax enhancements to these types of Web pages can greatly improve their experiences.
AJAX pros and cons
AJAX is rapidly becoming an integral part of several websites, several well established brands online now use AJAX to handle their web applications because it provides better interactivity to their users, this is due to the fact that implementing AJAX on a website, does not require a page to be reloaded for dynamic content on web pages. While there are numerous reasons to switch to AJAX there are quite a few matters that would make you reconsider using this combination of technologies as well. Below are some of the advantages and disadvantages of using AJAX.
This is pretty much the most striking benefit behind why several developers and webmasters are switching to AJAX for their websites. AJAX allows easier and quicker interaction between user and website as pages are not reloaded for content to be displayed.
AJAX applications on websites can be built to allow easier navigation to users in comparison to using the traditional back and forward button on a browser.
With AJAX, several multi purpose applications and features can be handled using a single web page, avoiding the need for clutter with several web pages.
Backed by reputed brands
Another assuring reason to use AJAX on your websites is the fact that several complex web applications are handled using AJAX, Google Maps is the most impressive and obvious example, other powerful, popular scripts such as the vBulletin forum software has also incorporated AJAX into their latest version.
The back and refresh button are rendered useless
With AJAX, as all functions are loaded on a dynamic page without the page being reloaded or more importantly a URL being changed (except for a hash symbol maybe), clicking the back or refresh button would take you to an entirely different web page or to the beginning of what your dynamic web page was processing. This is the main drawback behind AJAX but fortunately with good programming skills this issue can be fixed.