Glossary
Package manager
The tool that installs, updates and removes software.
A package manager installs software with its dependencies from signed repositories, tracks what belongs to what, and keeps everything upgradable with one command. apt on Debian and Ubuntu, dnf on Fedora and RHEL, pacman on Arch, apk on Alpine.
The concepts transfer between them: refresh the catalog, resolve dependencies, install from a trusted repository, and remove cleanly. Installing software by downloading random binaries bypasses all of that — and all of its security.
See it in practice
$ apt list --installed 2>/dev/null | wc -lCounts every package the manager is tracking — a few thousand on a typical system, all upgradable with one command.
Where you'll meet it
Search, install, upgrade and remove packages — plus the dnf/pacman equivalents.
Distribution (distro)The kernel plus everything else, packaged as a usable system.
sudo & suTemporary privilege, audited — and why sudo won everywhere.