A page that changes and/or creates its content on the browser, typically based on the users input/feedback/response.
The most popular way to create a dynamic content right now is AJAX. Search for "AJAX Tutorials" or "AJAX Examples" on Google and you will get tons of results.
> what is dynamic web page
A web application normally consists of two types of web pages -- static web pages and dynamic web pages.
In the case of static pages, the content served by the web server in the event of that page being requested is the same across all clients (as long as the content remains unchanged). In the case of dynamic web pages the content served to the client depends on the request parameters sent along with the request object.
A dynamic web page is normally created using a server side technology / language like J2EE / PHP / ASP etc. which is interpreted at the server and served to the client in a format specified by the content type header. A typical example of a static web page would be the 'credits' page of a web site which would more or less remain static. Compare this with a web site search feature in which the page being rendered after the search depends on the query being made by the client.