Yum is a software package management utility used in many popular Linux distributions, including Red Hat Enterprise Linux, Fedora, and CentOS. It is a front-end for the RPM package manager, meaning that it manages packages in the .rpm file format. Yum is used to install, update, remove, and manage software packages from official software repositories, as well as other third-party repositories. It works through the use of software repositories, which are special directories that hold collections of software packages. Yum performs dependency resolution when installing, updating, and removing software packages.

Some commonly used commands for Yum include:

• yum install: Installs the specified packages
• yum remove: Removes the specified packages
• yum search: Searches package metadata for keywords
• yum info: Lists description
• yum update: Updates each package to the latest version
• yum repolist: Lists repositories
• yum history: Displays what has been done previously with Yum

It is important to note that Yum is used in Red Hat Enterprise Linux versions 5 and later, while versions of Red Hat Enterprise Linux 4 and earlier used up2date. Additionally, Yum is not intended for use with Debian/Ubuntu systems, as they use different package management tools.