The -u or --untracked-files= flag to git status takes an additional parameter that is one of three values:
no: do not show untracked files
normal: show untracked files and directories
all: a more-verbose variant of normal
Omitting the additional word means the same as using -unormal (or --untracked-files=normal). So normal is the default, while no suppresses them entirely.
The additional verbosity with all simply takes the form of enumerating every file within an untracked directory:
$ git status
...
Untracked files:
(use "git add <file>..." to include in what will be committed)
weeble/
no changes added to commit (use "git add" and/or "git commit -a")
$ git status -uall
...
Untracked files:
(use "git add <file>..." to include in what will be committed)
weeble/file1
weeble/file2
Normally, -u (aka -unormal) has no effect on git status. However, if you change your defaults (by, e.g., setting status.showUntrackedFiles to no), -u will make git status display untracked files, i.e., override your modified default.