Here are some abbreviations common to my diary or the ttc world:

Symbol - What It Means

2WW - Two-Week Wait (having ovulated, now waiting to see if the egg gets fertilized!)
AF - Aunt Flo (Aunt Flow) (your menstrual period)
BBT - Basal Body Temperature
BC - Birth Control
BCP - Birth Control Pills
BD - Baby Dancing (sexual intercourse when fertile)
C# - Cycle Number (how many menstrual cycles have you been at it)
CD - Cycle Day
CF - Cervical Fluid
CM - Cervical Mucus
DH - Dear/Darling Husband (I try not to use this one)
DPO - Days Past (Post) Ovulation
Dr - Doctor
EDD - Estimated Due Date
EW, EWCM - Egg White Cervical Mucus
FF - Fertility Friend (an online charting sites)
IUI - Intra-Uterine Insemination
IVF - In-Vitro Fertilization
LP - Luteal Phase
LSP - Low Sperm Count
MF - Male Factor
O - Ovulate, Ovulation
O'ing - Ovulating
OB/GYN - Obstetrician/Gynecologist
PCOS - Polycystic Ovarian Syndrome
PG - Pregnant, Pregnancy
PI - Primary Infertility
RE - Reproductive Endocrinologist (fertility specialist)
SA - Semen Analysis
TCOYF - Taking Charge of Your Fertility (a book about TTC by Toni Weschler); also one of the more popular online charting sites
TTC - Trying to Conceive
UR - Urologist
US, U/S - Ultrasound