Javascript is a programming language that lets you do things on a web page without having to load the page again. This can mean anything from checking someone has put an email address in a contact form correctly to fancy animation effects. AJAX is a way of using Javascript to get information from the webserver without loading the whole page again. Google maps rely heavily on Javascript.

I have made an AJAX powered calendar (which shows which watch is on day shift in the Northern Ireland Fire and Rescue Service).