Ubuntu Restricted Extras is a software package for the computer operating system Ubuntu that allows the user to install essential software which is not already included due to legal or copyright reasons.
It is a meta-package that installs: The software in this package is not included in Ubuntu by default, as Ubuntu maintainers wish to include only completely free software in out-of-the-box installations.
Included packages may be closed-source, encumbered by software patents, or otherwise restricted.
For example, the Adobe Flash plugin is a closed-source piece of software.
[1] The Ubuntu Restricted Extras is a metapackage and has the following dependencies:[2] Starting with Ubuntu 10.10, several of these dependencies are included indirectly via another meta-package ubuntu-restricted-addons which is included by default.