• RPM (Red Hat Package Manager) is an default open source and most popular package management utility for Red Hat based systems like (RHEL, CentOS and Fedora). The tool allows system administrators and users to install, update, uninstall, query, verify and manage system software packages in Unix/Linux operating systems
• A package consists of an archive of files and meta-data used to install and erase the archive files. The meta-data includes helper scripts, file attributes, and descriptive information about the package. Packages come in two varieties: binary packages, used to encapsulate software to be installed, and source packages, containing the source code and recipe necessary to produce binary packages.
• ‘deb’ is not a command. It is used in sources.list file to indicate a Debian software repository. From Ubuntu Man page – sources.list: The source list is designed to support any number of active sources and a variety of source media.

pros/cons of deb and rpm:

• Rpm is ‘Standardized’ (not that there isn’t a deb spec)
• Rpm is used by many different distributions (but packages from one do not necessarily work on another)
• IIRC allows dependencies on files, not only on packages
• In the RPM world, all your packages (the RPMs you maintain) are located in something like ~/rpmbuild. Underneath, there is the SPEC directory for your spec-files, a SOURCES directory for source tarballs, RPMS and SRPMS directories to put newly created RPMs and SRPMs into, and some other things that are not relevant now.
• Deb is Growing popularity
• Deb is  Allows recommendations and suggestions (possibly newer RPM allows it as well)
• Main difference for a package maintainer (I think that would be ‘developer’ in Debian lingo) is the way package meta-data and accompanying scripts come together
• rpms can’t have a dependency on “package X OR package Y”. You can can achieve the same effect with…
• rpms allow you to depend on a file instead of a package.