ajaxAjax (Asynchronous JavaScript + XML) is very trendy nowadays.
I posted an example (italian zip code search) two months ago and I want to write some other simple examples.

This is a minimal Ajax script, a simple echo service with delay.
The text you write is sent to the server and worked out by a php script, after 2 seconds the text is returned and then displayed to the client.
All the operations are asynchronous, you can see a loading red message (like gmail, to provide a feedback to the user when your browser is processing some data).

Write something and change the focus:

You said (2 seconds delay):