AK: (1) n. Avada Kedavra, the Killing Curse. (2) v. Avada Kedavra – to kill someone.
AK'd (AK-d, AK'ed, AK-ed): v. Past tense of AK.
AD: n. Albus Dumbledore or, more commonly, Aberforth Dumbledore, brother to Albus.
AP: n. Aunt Petunia.
CC: n. Cruciatus Curse.
C!M: n. A reference to Barty Crouch jnr. when under transformation of the Polyjuice Potion.
CoS, (CS): (1) n. Chamber of Secrets, the second book in the series. (2) n. A Chamber of Secrets in Hogwarts, hidden by Salazar Slytherin. via one of the girls's bathrooms.
DA: n. Dumbledore's Army, a group of Hogwarts students led by Harry Potter to learn magical defensive techniques.
D'Dore: n. Dumbeldore, Albus.
DD: (1) n. Dumbledore (Albus). (2) n. Dudley Dursley.
DE: (pl. DEs): Death Eater, servants of Lord Voldemort.
DH: Deathly Hallows, the seventh book in the series. *
DIGS: An acronym for: Dumbledore is Giant Squid. A theory that the two characters are one and the same.
DP: n. Daily Prophet, The. The wizarding world's leading newspaper.
FB (FBAWTFT): Fantastic Beasts and Where to Find Them, a book made for charity that details certain magical animals.
F&G (F+G): n. pl. Fred and George Weasley, older brothers to Ron. See Twins.
GG: n. Godric Gryffindor. Hogwarts founder, namesake of Gryffindor House.
GP: n. Grimmauld Place, the home of the late Black family and the Headquarters of the Order of the Phoenix. See No.12 and OotP.
GoF (GF): Goblet of Fire. (1) Fourth book in series. (2) A Goblet featuring in the fourth book, from which the names of the Triwizard Champions came.
HB: n. Head Boy.
HBP: Half-Blood Prince. (1) Sixth book in series. (2) Person who is the Half-Blood Prince.
HE (pl. HEs): n. House Elf.
HG: (1) n. Hermione Granger. (2) n. Head Girl.
HoH: n. Head of House – the member of staff who is Head of their particular House.
HP: Harry Potter. (1) n. The series of the books. (2) n. The person.
LM: n. Lucius Malfoy, DE and father of Draco Malfoy.
LV: n. Lord Voldemort.
MEM: n. Mad-Eye Moody.
MM: n. Minerva McGonagall
MoM: (1) n. Minister of Magic. (2) n. Ministry of Magic.
MWPP: n. pl. Moony, Wormtail, Padfoot and Prongs. The nicknames of the Maurauders, or (in respective order) Remus Lupin, Peter Pettigrew, Sirius Black, James Potter.
No.12: n. Number Twelve Grimmauld Place. the home of the late Black family and the Headquarters of the Order of the Phoenix. See GP and OotP.
OBHWF: One big happy Weasley Family
OT: Off topic *
OotP (OP, OtP): Order of the Phoenix. (1) Fifth book in series. (2) Organisation led by Albus Dumbledore, main focus is defeating Lord Voldemort.
PoA (PA): Prisoner of Azkaban. (1) n. Third book in series. (2) n. The person, Sirius Black.
PP: n. Peter Pettigrew.
PS: Philospher's Stone. (1) First book in series. (2) The stone itself, as made by Nicholas Flamel.
QTA (QTTA): Quidditch Through The Ages.
QWC: n. Quidditch World Cup, and event that takes place every four years.
RL: Real life. *
RR: n. Rowena Ravenclaw. Hogwarts founder, namesake of Ravenclaw House.
RW: n. Ron(ald) Weasley.
S.P.E.W.: Hermione's Society for the Protection of Elvish Welfare.
SS: n. (1) Salazaar Slytherin. (2) Sorcerer's Stone, the American (Scholastic) title for the First book. See: PS. (3) n. Severus Snape, Potions master at Hogwarts. Also member of the Order of the Phoenix, and former Death Eater.
SWM: n. (1) Chapter heading in Harry Potter and the Order of the Phoenix (Ch. 28). (2). Snape's pensieve memory which Harry saw.*
TLC: (1) n. The Leaky Cauldron, a public house in Diagon Alley. (2) n. A FANTASTIC Harry Potter website.
TR: n. Tom Riddle, the boy (man) who became Lord Voldemort.
Twins, The: n. pl. Fred and George Weasley. See F&G.
TWT: n. Triwizard Tournament. A tournament of three tasks between the three large wizarding schools, Hogwarts, Durmstrang and Beauxbatons.
UV: n. Uncle Vernon.
VD: [rare] n. Voldemort, Lord.
Voldy (Voldie): n. Lord Voldemort.
VWI: n. Voldemort War One, also known as the First War. Occurred between c. 1970 and 1981.
VWII: n. Voldemort War Two, also known as the Second War. Started in 1995, after the rebirthing of Lord Voldemort.
WT: n. Wormtail, also known as Peter Pettigrew.
WWN: n. Wizarding Wireless Network, a radio station for magical folk.

12GP - Number 12 Grimmauld Place
DADA - Defence Against the Dark Arts
GH - Godric's Hollow
L&J - Lily and James

LEXUS = LEXicon Steve & Us (fan club for Steve of the HP Lexicon)
MAFIA = Melissa Anelli's Fans In Action! (fan club for Melissa)
PCAA= Potter Cast Addicts Anonymous
SQUEE = Sue's Quite Unnervingly Excitable Enthusiasts (fan club for Sue)
S.P.E.W. = Sensational PotterCast Elves Worshippers (fan club for the Leaky elves who transcribe the Pottercasts)