Hallyu (Korean Wave) = the increase in the popularity of South Korean culture around the world, similar to Cool Japan
bias = favorite member in all of K-pop or in a group (I don't actually use this term or know how to)
idol = K-pop celebrity, kind of like Japanese idols or the ones in animes
group = the standard K-pop unit that usually consists of 5 members on average, there are some with less or more
sub-unit = a unit created from certain members of the main group, they usually have a different style/promote different music than the original group
leader = usually, but not necessarily, the oldest member in the group, given more responsibilities, looks after other members
maknae = the youngest member in a group
comeback = when a group/artist has a new album or release and they promote it on the Korean music programs
Big 3 = S.M., YG, and JYP are the three largest companies
ent = abbreviation for Entertainment company, such as SM Ent, YG Ent, and JYP Ent
sasaeng fans = crazy, stalker fans that try to follow their idols and interrupt their private lives, some not considered fans as they even try to harm these celebrities
spazz(ing) = being generally hyper/crazy and excited when discussing a topic
oppa = older male for a female, big brother
unnie = older female for a female, big sister
hyung = older male for a male, big brother
noona = older female for a male, big sister
saranghae(yo*) = I love you, to love
annyeong(haseyo*) = hello, greeting
*makes it more polite
Group Name Acronyms/Descriptions:
SNSD = So Nyeo Shi Dae (Korean)/ Shojo Jidai (Japanese) / Girls' Generation (English) / meaning is "The generation of girls' domination has come." / often shortened to SoShi
TVXQ/DBSK = Tong Vfang Xien Qi (Chinese) / Dong Bang Shin Ki (Korean) / Tohoshinki (Japanese) / roughly translates to "Rising Gods of the East"
2NE1 = pronounced "to anyone" or "twenty one" / meaning is "21st century" or "new evolution"
f(x) = mathematical function, 'f' is for "flower" and 'x' is for "X chromosome"
T-ARA = pronounced "tiara"
2AM/2PM = used to be one group called One Day but later split
Sources:
Personal knowledge
Wikipedia
Urban Dictionary
Yahoo! Answers
My little sister (learning Korean and also a huge K-pop fan)