Abbreviations you might see...

RTA = Rose Talk Australia (not Roads and Traffic Authority ... might be shortened to RT)
OGR = old garden rose
OP = open pollinated
HMF = Help Me Find: http://www.helpmefind.com/gardening/plants.php
RMV = rose mosaic virus
BS = Black spot (and NOTHING else )
PM = Private message (or powdery mildew... depending on the context).
Sp.= species
DA = David Austin
HT = Hybrid Tea
HP = Hybrid perpetual
HM = Hybrid musk

I can't actually think of any more. If I've forgotten any please add them or ask what something means and I'll add it