Dynamic web template and master page

Question

HI,
What is the difference between the Dynamic Web Template that I create in Expression Web and Master page that is created in ASP.NET, This is because in both cases I created a page and it could be used by the user to add contents as per his wish. In Dynamic web template also we define a area for the user to add content as we have content place holder in ASP.NET so what is the key difference in both ?