$ man path

PATH

An environment variable that tells the terminal where to find executable programs.

by Shawn Tenam

When you type git or python or node, the terminal searches the folders listed in PATH to find that program. If a command returns "not found" even though you installed it, the problem is almost always PATH. The terminal does not know where the program lives. Understanding PATH saves hours of debugging "command not found" errors.

echo $PATH shows your current PATH. Each folder is separated by a colon. When you install something with Homebrew, it adds the install location to your PATH. If you get "command not found" after installing something, run hash -r to refresh the shell cache or open a new terminal session.