Work with hybrid and Web Forms page templates
When working with Web Forms, you base your page templates on .master files and define the appearance and style of the page by setting the template and the theme. Hybrid mode lets the template and all pages, based on it, use both MVC widgets and Web Forms widgets on the same page. Thus, if you have legacy pages with Web Forms widgets, say with Forums, you can still take advantage of MVC technology benefits.
For more information, see Page templates.