There are two types of Fedora system; "traditional", which use DNF, and "image-based" which use rpm-ostree.
On a traditional Fedora system, software is divided into RPM packages, which can be managed via DNF.
The "Atomic" variant of Fedora uses rpm-ostree to update the host.
rpm-ostree is a hybrid image/package system. By default, installations are in "image" mode using OSTree, but additional packages can be installed. It also supports overrides, rebases, and many other features. For more information, see its online documentation.
atomic CLI supports installation of system containers, which are Docker/OCI images distinct from the host user space. For more information, see its online documentation.