A canonical example of a command is an external binary executable located somewhere on a filesystem (such as in /bin), which may be invoked merely by typing its name on the command line thanks to the PATH resolution.
, provided its containing directory is in the PATH.
A command is any meaningful shell word. typing
Command is any meaningful shell word like an shell keyword, alias, shell function, etc. In the sense of being an executable, it always executes in a subshell, i.e. in a new (child) shell environment.