From LSDevLinux

Packaging is the process by which pieces of software are turned into installable "packages" for various Linux distributions (and other systems, such as Mac OS X and OLPC).

There are two aspects to this:

1. Initial creation of the package
2. Ongoing maintenance as a result of
   1. Upstream upgrades
   2. Distro upgrades

In this context, "upstream" refers to the original source of the software, before it is packaged. Usually this will be a developer's tarball or source-control repo.

Once a package has been created, the control files that are used to describe and build the package can be re-used for the ongoing maintenance work with very little extra effort. Initial creation and ongoing maintenance may therefore be done by different people.

A tutorial for making packages for Debian-based systems (especially Ubuntu) is in Packaging using Pbuilder.