There are three different features for packaging Web sites in Office SharePoint:
1.Back up and Restore a site (.cmp)
2.Create a Web package(.fwp)
3. Save a site as a site template using browser (.stp)
.cmp file : stands for content migration packages
.fwp file : stands for feature web packages
.stp file : stands for site template file
1.Back up and Restore a site (.cmp): when you want to move an entire site or subsite to another server or location use back up and restore, but they can't move customizations, settings,workflows, alerts, Recycle Bin state and objects inside.
2.Create a Web package (.fwp): Web packages are a great way to duplicate site structure, but they cannot include list data, subsites, or security and permissions settings.
3. Save a site as a site template using browser (.stp): When you want Subsites created on a site to have a similar site structure, look and feel, and even content. You can do this by saving a site as a site template and adding it to the Site Template Gallery so that anyone can use the site as a template, but they can't include list data.