Glossary
Distribution (distro)
The kernel plus everything else, packaged as a usable system.
Linux itself is only the kernel. A distribution bundles it with GNU tools, a package manager, an init system, drivers and defaults to make a usable operating system: Ubuntu, Debian, Fedora, Arch, Alpine.
They differ in package manager, release cadence and defaults — but the commands in this reference behave the same across all of them. That portability is exactly why terminal skills outlive any particular distro choice.
See it in practice
$ cat /etc/os-releaseNames the distribution and version. The first command to run on any machine you did not set up yourself.
Where you'll meet it
Search, install, upgrade and remove packages — plus the dnf/pacman equivalents.
KernelThe core of the operating system, managing hardware and processes.
Package managerThe tool that installs, updates and removes software.