BL = Back Loop, block, or bobble, depending on the context. .
ch = chain
chs = chains
cl = cluster
dc = double crochet
dtr = double treble crochet
FO = finished object
FP = front post
g = gram
half dc = half double crochet
hdc = half double crochet
inc = increase
incl = include / including / inclusive
m = meter; also mesh
oz = ounce / ounces
p = picot
pat = pattern
pc = popcorn
rep = repeat
rnd = round
rnds = rounds
sk = skip
sp = space
sps = spaces
st = stitch
sts = stitches
tog = together
tr = treble crochet / triple crochet
tr tr = triple treble crochet
UFO = unfinished object
YO = yarn over
* = The pattern will specify how many times to repeat a series of instructions following an asterisk, or between asterisks.
( ) = The pattern will specify how may times to repeat a series of instructions that are given inside the parentheses.
[ ] = The pattern will specify how many times to repeat a series of instructions that are given inside the brackets.
“ = inches