A postback occurs when the browser makes a type of request to the webserver.
This causes :
1. Data to be sent from the browser to the webserver.
2. Processing on the webserver.
3. A response from the webserver back to the browser (i.e. a new web page).
Lots of things like database access, and filesystem cannot happen directly
in the user's browser. Those things occur on the web server.
So, if you wanted a bit of text (like a username) to be pulled from a
database and written to the browser when your user clicked a button, you
would want the buton to cause a postback. During the postback your program
would be able to talk to the database, and put the value retrieved into the
new webpage to send back to the user.
Doug