YUM (short for Yellowdog Updater Modified) is an open source tool that was developed by Red Hat Inc for RPM-based systems. It is a high-level package management tool that's used for easily installing, removing, updating, or searching software packages on systems or in network repositories. It allows us to use a CentOS base and third-party repositories that are created on remote or local servers to install individual packages or groups of packages automatically, after resolving their dependencies.
In upcoming versions, YUM is being replaced by DNF (which is compatible in its command set). YUM has already been replaced with DNF (Dandified YUM) as the main package manager in Fedora.