SharePoint master pages are similar to layout pages in ASP .net , Its used for creating a unique look and feel for pages. Common elements in SharePoint master pages are,
- Top Navigation,
- footer ,
- Site actions .. etc.
When we view a SharePoint page in browser, the content page and master page are merged together and render as single page. Master page ac as a container for the contents in a page.
Master Pages and Content Pages
This illustration will give you an idea about SharePoint master pages and Content pages.
an example for master page is given below,