What does aux mean in ps aux?

linux shell

ps aux seems to conveniently list all processes and their status and resource usage (Linux/BSD/MacOS), however I cannot comprehend the meaning of parameter aux using man ps.

What does aux mean?

a = show processes for all users
u = display the process's user/owner
x = also show processes not attached to a terminal

By the way, man ps is a good resource.

Historically, BSD and AT&T developed incompatible versions of ps. The options without a leading dash (as per the question) are the BSD style while those with a leading dash are AT&T Unix style. On top of this, GNU developed a version which supports both styles and then adds to it a third style with options that begin with double dashes.

All (or nearly all) Linux distributions use the GNU ps utility. The above options are as defined in the GNU man page.

In the comments, you say you are using Apple MacOS (OSX, I presume). The OSX man page for ps is here and it shows support only for AT&T style.