A queer -- that is gay, lesbian, bisexual, transgendered or questioning -- tween, teenager or young adult.
Used as an abbreviation occasionally from the 1980s onwards. Most probably started with social services agencies and others working/dealing with queer youth and their issues in community, counselling and school settings where matters of sexual identity might not be fixed or agreed upon with the subject, or there was concern about inadvertent outing of the subject (thus, used as a tacit code for additional confidentiality).
Occasionally used by individuals to avoid outing (also spelled: outting) a teen or adult.
Rarely used outside of notes and official communications.
Marta is a cool q-kid, very self-confident and out there -- ITL.
Joe is a 16 y.o. q-kid (not self-identifying), displaying behaviour patterns symptomatic of incipient A/D (alcohol/drug) addiction possibly related to identity issues combined with peer pressure.