A vowel appearing in the Norwegian alphabet (among others) but not in English. ø is pronounced "uh," like the "u" in "hurt."
The symbol ø appears in the other users nodelet to label users who have turned off the chatterbox.
Character info:
ISO Latin 1 character code: 248 (uppercase is 216)
Html entity: ø (uppercase is Ø)
TeX character: \o (uppercase \O)