AP = The name of a series of nymphs, AP can stand for either "All Purpose" or
"Andre Puyens" depending on who you talk to.
EHC = Elk Hair Caddis
Some other common abbreviations:
PT - pheasant tail
BH - bead head (can be combined BHPT = bead head pheasant tail)
GRHE - gold ribbed hare's ear
P & O - partridge and orange.