Package manager. Package managers are responsible for managing your installed software. There are a variety of options, and distros typically will choose one as their default. Pacman for Arch, Aptitude for Debian, RPM for RedHat, and others. These are mostly interchangeable for the end user, but each has slightly different commands and frontends. So just be aware there will be a bit of an extra learning curve moving from a distro that uses one to a distro that uses another.
RedHat uses dnf, RPM is the package format.
Apt sucks, pacman is ok, dnf is the best, history and rollback are great.