Glossary
Environment variable
A named value processes inherit when they start.
Environment variables are KEY=value strings handed to every process at launch: PATH lists where to look for commands, HOME is your directory, EDITOR your preference, and applications commonly read their configuration (DATABASE_URL, API_KEY) from them.
Inheritance is a copy made once, downward: children receive the parent's environment, and nothing a child changes flows back. export promotes a shell variable into the environment; without it, the variable stays private to the shell.
See it in practice
$ DEBUG=1 ./appSets a variable for exactly one command. It exists for that process and disappears afterwards — no export, no cleanup.
Where you'll meet it
How configuration flows into processes — PATH, export, and why edits "don't stick".
PATHThe ordered list of directories the shell searches for commands.
ProcessA running program, with its own ID, memory and environment.