Technically a .CAB file, but Its not like the .CAB file we used in 2003.
Now you would use a Solution, which is a .CAB file with a .wsp
extension. Solutions contain a manifest that describes what needs to be
installed where and can be used to automatically install Features,
webparts, files, Code Access Security policies, event receivers, etc. to
every web Front end on a scheduled basis. If you are installing web
parts you can either install them directly with the solution, in which
case they go in the Server (web Application) gallery or put them in a
feature to install them to the Site Collection gallery.
Take a look at the following:
msdn2.microsoft.com/en-us/library/ms413687.aspx