From LQWiki

Overview

Most Linux systems organize their component programs into packages, each of which is comprised of one or more related programs and associated configuration or metadata files. As it happens, there are a number of more or less incompatible kinds of package, each with its own package manager program(s). Some of the more common ones:

1. RPM (RedHat Package Manager): used on RedHat, Fedora, CentOS and perhaps other distributions.
2. .deb: used on Debian and derivative distributions such as Ubuntu.
3. portage: used on Gentoo

See also

End User Manual:Package Maintenance and Update