Read this http://code.google.com/apis/analytics/docs/tracking/asyncTracking.html I hope it'll help you.
The latest version of the Analytics tracking code offers an improved way to track website visitors with Google Analytics. It takes advantage of browser support for asynchronous JavaScript to enhance the speed in which the tracking code is loaded. With the latest version of the tracking code, you can also place the Analytics snippet higher in the page without delaying subsequent content from rendering.
Asynchronous tracking is the tracking which can be done at the same time as rendering the other content.
Asynchronous Tracking is a Google Analytics code given to webmasters that want to keep track of their websites' stat.
Google Analytics takes advantage of browser support for asynchronous JavaScript to enhance the speed in which the tracking code is loaded. With the latest version of the tracking code, you can also place the Analytics snippet higher in the page without delaying subsequent content from rendering.In simple words Asynchronous Tracking is a Google Analytics code given to webmasters that want to keep track of their websites' stat.