I'm not certain, but I think there may be an explanation of some of the shortcuts under the FAQ section. Some are breed shortcuts like:
RIR Rhode Island Red
NHR New Hampshire Red
RSL, BSL Red Sex Link, Black Sex Link
SLW, GLW Silver Laced Wyandotte, Gold laced Wyandotte
BR Barred Rock
BO Buff Orpington
OEGB, MGB Old English Game Bird, Modern Game Bird
Others are abbreviations for commonly used words/terms like:
PVS PolyViSol pediatric vitamins used for sick chickens
EVOO Extra Virgin Olive Oil
ACV Apple Cider Vinegar
DE Diatomaceous earth
Others are for people such as:
DH, DW, DD, DS, DM, DF, MIL, FIL, -- Dear: husband, wife, daughter, son, mother, father, mother-in-law, father-in-law, etc.
ETA: forgot an important one: DUW -Dial Up Warning! Means post is picture heavy or may be slow to load on a dialup connection