I am trying to understand `info who` but completly fail at the term »*non-option argument*«. Can someone please explain this term to me in simple words or an example?

**UPDATE**: from ' info who' :

> If given **no non-option arguments**, `who' prints the following
> information for each user currently logged on: login name, terminal
> line, login time, and remote hostname or X display.
> 
> If given **one non-option argument**, `who' uses that instead of a
> default system-maintained file (often `/var/run/utmp' or `/etc/utmp')
> as the name of the file containing the record of users logged on.
> `/var/log/wtmp' is commonly given as an argument to `who' to look at
> who has previously logged on.
> 
> If given **two non-option arguments**, `who' prints only the entry for
> the user running it (determined from its standard input), preceded by
> the hostname. Traditionally, the two arguments given are `am i', as
> in `who am i'.

I [thought to] know the difference between an argument and an option, but this [again] nixes a lot.