Ajax stands for Asynchronous JavaScript and XML.

Example of Ajax : Google’s Maps, Google’s Gmail, or any live support system.

Brief : Ajax is the way for website pages to send and receive data from/to website on particular time interval. It doesn’t need end user’s attention and no need to wait for new page load or click on somewhere on webpage to get updated values. This is how it is called Asynchronous. Ajax increase the webpage's speed and usablity.

Browser Support : Internet Explore (IE) , Firefox, Opera, Safari

• XHTML/HTML and CSS
• to exchange data from/to the website, Ajax uses an object called XMLHttpRequest. Sometime Ajax uses another object called IFrame for the same purpose.

• Generally user has to submit form and wait for few seconds to get response from the web server. This is the way the traditional web application behaves. Load data on user request- execute webpage event handlers and then execute functions to process the user request. Ajax has reduced such unwanted bandwidth consumption.
• Without interfering rest pages and user effort to request for the updated data, Ajax pushes/pulls information to/from web server for the active webpage at intervals. Thus your website works in real-time.

Precaution:

• Take care while you use Javascript: To should test the website in different browsers (or versions) to check its compatibility.
• There may be delay due to network traffic or any other issue. In such scenario user never know that the current piece of data is updated or not. It is suggested to user some visual feedback to re-adjust the user’s eyesight.