async-shell-command is an interactive compiled Lisp function in `simple.el'.

It is bound to M-&.

(async-shell-command COMMAND &optional OUTPUT-BUFFER ERROR-BUFFER)

Execute string COMMAND asynchronously in background.

Like `shell-command', but adds `&' at the end of COMMAND
to execute it asynchronously.

The output appears in the buffer `*Async Shell Command*'.
That buffer is in shell mode.

You can configure `async-shell-command-buffer' to specify what to do in
case when `*Async Shell Command*' buffer is already taken by another
running shell command. To run COMMAND without displaying the output
in a window you can configure `display-buffer-alist' to use the action
`display-buffer-no-window' for the buffer `*Async Shell Command*'.

In Elisp, you will often be better served by calling `start-process'
directly, since it offers more control and does not impose the use of a
shell (with its need to quote arguments).