It means one-night-stand so they are only interested in having sex for the night.
In the personal ads that I have seen, LOS means Lost or Stolen.
Androgynous
For sex :)
Long Term RelationshipLTR in personal ads means long term relationship.
ads-on may be a reference to add-ons, I believe? Add-ons are self explanatory, so they literally add on to something, whether it may be a game or a report.
professional
water sports
OHAC mean in Relationship
friends with benefits.
In Search Of
Pay to play
Bareback, or no condom