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.
Errors that come down to this concept: bash: command: command not found