Otaku - Anime newcomers like to consider themselves "otaku" when they start liking anime; their definition of otaku is anime fan. Long-time anime fans, however, tend to not call themselves otaku because of its negative Japanese connotation. The literal translation of the word is your house, but in Japanese slang, this refers to somebody who has an obsessive hobby. I do consider myself an otaku because I kinda do have an obsession with anime.

Hikikomori - A hikikomori is someone who secludes themselves within their home, sometimes refusing to leave their home at all in an effort to isolate themselves from society. They have someone paying their bills. It can be viewed as a social phobia similar to agoraphobia. Hikikomori are often associated with otaku, but the terms are distinct. Hikikomoris don't have to instead in anything, they basicly just fail at life. The anime 'Welcome to the NHK' shows what it is like to be a Hikikomori.

NEETs - I've only ever it written like that. A NEET(Not in Employment, Education, or Training) is a bit a an Otaku mixed with a Hikikomori. They have someone paying their bills, parents most likely and they may or may not  have an obsession with something. Princess Jellyfish has examples of NEETs.

Seiyū - Japanese voice actor

Ahoge - refers to the single hair that sticks out of the character's hair. Literally meaning 'stupid hair' it tends to point out the characters that are stupid, but there are exceptions like Edward Elric from Fullmetal Alchemist.

Antenna hair -  in which there are two or more locks of hair sticking up as opposed to one.

Fan service - Parts of the story or show that are there purely for the fan and could otherwise not be in the show because it has zero effect on the plot/storyline. Could be something funny or something sexual.

Shotacon -A genre of manga and anime wherein childlike male characters are depicted in an erotic manner.

Lolicon - A genre of manga and anime wherein childlike female characters are depicted in an erotic manner.

OVA - Original Video Animation. Usually just specials on DVDs.

Uke - "Passive" partner in Boys Love/yaoi. Tend to be smaller, inexperienced, younger, and sometimes may even had been straight before hand. But I've seen Uke that have broken all those and it kinda confused me at first.

Seme -"Dominant" partner in Boys Love/yaoi. Tend to be bigger, experienced, and older. Of course I've seen some that don't fit that.

Onee-chan- Older sister, with "onee" meaning older sister and "-chan" being an affectionate suffix. The beginning "o" is a respectful honorific.

Onee-sama - Older sister, with "onee" meaning older sister and "-sama" being a respectful suffix. The beginning "o" is another respectful honorific.

Onii-chan - Older brother, with "onii" meaning older brother and "-chan" being an affectionate suffix. The beginning "o" is a respectful honorific.

Onii-sama - Older brother, with "onii" meaning older brother and "-sama" being a respectful suffix. The beginning "o" is another respectful honorific.(similar to Onii-san)

Moe - A character said to be moe causes a protective instinct or feelings of affection. The closest definition in other languages would be "Fetish", but it is not. Does not necessarily have a direct correlation to sexual preferences. It is more about the attractive qualities, both physical and personality, in any capacity: Friend, Sister, Daughter, Mother, etc. Moe can also refer to said feelings. It can be used to refer to a love of a specific trait, such as meganekko-moe ( "glasses-girl" moe), a love of girls wearing glasses.

Mangaka - Creator of the manga. The mangaka is often the writer and the illustrator of the work.

Gothlol - Gothic Lolita—A fashion trend where girls and young women dress in the style of elaborate porcelain dolls.

Eyecatch - A scene or illustration used to begin and end a commercial break in a Japanese TV program, similar to how bumpers into/out of commercial breaks are used in the United States.

Ecchi -The Japanese Pronunciation of the letter "H". It represents the first letter in the word "Hentai" and can refer to anything ranging between mildly erotic manga and anime to unwarranted sexual behavior.

Bishōjo - Literally, "pretty girl". Often refers to any young, attractive woman, but also used to imply sexual availability

Bishie - slang for an incredibly cute/beautiful guy that mobs of girls like to chase after.

Bishōnen - "Beautiful boy"—Japanese aesthetic concept of the ideally beautiful young man. Androgynous, effeminate or gender ambiguous. In Japan it refers to youth with such characteristics, but in the west has become a generic term for attractively androgynous males of all ages.

Dere Dere -Meaning to become "lovestruck", "lovey dovey".   Dere Dere has several sub-archetypes eventually spawned after certain variations of character kept showing up more and more. Those types are tsundere, yandere, kudere, kamidere, himedere, and dandere. All these types tend to be girls, but can be boys as well.

Tsundere -The progression of a character personality from cold and hostile to eventually displaying their warm and loving side.  I see this one come up the most. Example: Akari Kirishima from Nyan Koi.

Yandere - a Japanese term for a person who is initially very loving, caring, and gentle to someone (or at least innocent) they really, truly like and care for a lot before their romantic devotion becomes mentally destructive in nature, often through violence and/or brutality. Example: A classical and rather extreme example of yandere is Yuno Gasai, from the manga/anime Future Diary, who is prone to kill anyone who may interfere with her obsessive passion for the series protagonist Yukiteru Amano (or just even be near him without any romantic contact at all). Yuno was a crazy bitch.

Kūdere - A character type, mostly of a female character, who is normally cold and unassuming but later reveals a softer and kinder side. Example: C.C. from Code Geass

Kamidere - They have a cold and hostile personality because they have a godlike superior and eventually become loving and warm. Kami means God. Example: Amber from Darker Than Black.

Himedere - Same as Tsundere, but with the reasoning being a princess like superior. Hime means princess. Example: I have no examples of this one.

Dandere - A character who is usually emotionless, that eventually changes to display their sweet, romantic, and loving soft side. Example: Yuki Nagato from Haruhi Suzumiya

I think that covers all the words I will use that you will have to know.