Portage is a package management system used by Gentoo Linux
Gentoo is sometimes referred to as a "meta-distribution" due to the flexibility of Portage which allows it to manage other operating systems as well. In addition to Gentoo Linux there exist Portage implementations for FreeBSD, Mac OS X and Sun Solaris.
Portage consists of a hierarchal tree of ebuilds (currently more than 10,000 in Gentoo Linux) and management utilities such as emerge and a suite of related tools packaged as gentoolkit. Ebuilds contain metadata about each package as well as the instructions on how to compile, install and configure a software package. Through the use of profiles and emerge, users and developers can use Portage to install and maintain the packages that make up the underlying operating system and the applications on a system.
Portage derives its name and general design from the BSD ports system of FreeBSD/NetBSD/OpenBSD. Traditionally ports is implemented as a complex tree of Makefiles. Both compile packages from source and allow users to safely install and uninstall software from a system and automatically handle dependencies. The intent behind Portage is to harness the strength of Python to create a next-generation ports system that is more powerful while being easier to use and maintain. A system managed by Portage can be compiled "on the fly". The act of installing Gentoo Linux from scratch involves setting up enough of a working compiler and build environment through which Portage can download source code from the Internet and build the rest of the "core" of the system and any desired applications. However, Portage does support the use of prebuilt packages for those wishing to quickly setup a fully working system.