Rpm is the acronym of RPM Package Manager: it is the low-level package manager in use in all the Red Hat family of distributions, such as Fedora and Red Hat Enterprise Linux.
An rpm package is a package containing software that is meant to be installed using this package management system, and rpm packages are usually distributed via software repositories.
This is a companion discussion topic for the original entry at https://linuxconfig.org/how-to-create-a-custom-rpm-repository-on-linux