The yum command no longer exists but is now an alias pointing to the dnf command.
Since the source code of the yum command had become a nightmare, RedHat decided to start a new project called dnf (Dandified Yum), following the same syntax.
The rewrite took several years.
According to several reports, the dnf command would be a lot faster than yum.
In addition, a new command called microdnf has been created. This is a subset of the dnf command used in the minimal UBI image. It only allows the installation, update and removal of packages.