.deb is a file format, nothing more. It originated in the Debian Linux project. Maemo is based on an ARM version of Debian Linux, and takes advantage of the .deb format.

It allows multiple files to be packaged together with metadata such as a list of files, descriptions, and (very importantly) dependencies.

If a .deb file says "in order to install me, you need to also get packages A, B, and C," that allows an installation program to fetch the needed dependencies and install them as well.

Some of those dependencies may be libraries or programs that end users should never see or even know about.

In order for dependency management to work, the related files have to be stored in some standard place and in a standard way. Voila: You have a repository.

The .deb format has been around for a long time, and is used by many different Linux distributions on many different platforms. You can't mix and match files indiscriminately. You're likely to get into trouble if you mix and match different releases, such as Maemo's mistral and bora, or Ubuntu's Feisty Fawn and Gutsy Gibbon, or Debian's sarge and etch.

By convention, there are clues in the filenames, but you don't have to know about that, because the repositories and package managers protect you from those ugly details.

The .install file's format and purpose is documented here:

https://stage.maemo.org/svn/maemo/pr...repository.txt