2525 cafe = a Nico Nico Douga cafe located in the Nico Nico Douga studio building headquarters in the heart of Ikebukuro district, Tokyo.
888888888 = a term used on Nico Nico Douga to mean applause or to clap. In Japanese the number 8 is pronounced as "hachi", which sounds close to "pachi" (パチ), which means "to applaud or clap".
Damatte Mylist (黙ってマイリス, lit. silent Mylist) = a tag on Nico Nico Douga that is put on videos where the number of comments is less (often significantly so) than the number of mylists.
GJ = a term used on Nico Nico Douga, short for "Good Job". It is usually used at the end of a video to congratulate the user for a good job on the video.
JD (usually in all capitals) = stands for Joshi Daigakusei (女子大学生) which means "college school girl", Likewise, JK stands for Joshi Kousei (女子高生), which means "high school girl", JC stands for Joshi Chuugakusei (女子中学生), meaning "middle school girl"; while JS stands for Joshi Shogakusei (女子小学生), meaning "elementary/grade school girl". Their equivalent terms for male students are DK, DC, and DS, with the "D" in each acronym standing for Danshi (男子), or male, instead of "Joshi"
jk = The letters "jk" (usually in lowercase to differentiate from JK) are also used as shorthand for many other different phrases in the Japanese internet community, but most commonly joushikiteki ni kangaete (常識的に考えて) which literally means "to think using common sense", but colloquially "if you think about it" or "seriously".
ktkr = stands for kitakore (来たこれ, lit. "It's here!", "It came!"), and is usually used when someone has been satisfied in watching a video or has been waiting for a user to upload something for a long time.
Motto hyouka sareru beki (もっと評価されるべき, lit. ought to have more attention) = is a phrase used on Nico Nico Douga to tag videos that users consider excellent but seem not to have as many views as they deserve. Variations include Motto Motto Hyouka Sareru Beki (もっともっと評価されるべき, lit. "ought to have much more attention") and Sotto Hyouka Sareru Beki (そっと評価されるべき, lit. "ought to have tons of attention")
Mylist (マイリスト) = A term used on Nico Nico Douga. Mylists are like a combination of a playlist and favorites. On Nico Nico Douga, you can create Mylists, which are a playlist of videos. Mylists can be for a list of favorites, a list of a user's own videos or for songs a user wants to use in choruses; utaite record all their covers in a Mylist seperate from all other videos. Mylists are crucial to Nico Nico Douga rankings and usually count for a fairly large portion of the grading and ranking calculations. On the English version of Nico Nico Douga, it is stylized as "My List".
namahousou (生放送) = is a live broadcast set up by a person at Niconico Live. Namahousous are 30 minutes by default, but users can pay with points to extend the length of their housou. This process is known as enchou (延長, lit. extension); thus, upon an enchou, viewers will congratulate the host with comments of "enchotsu" (えんちょつ). Namahousous can cover any kind of topic, from singing or gaming to just chatting. Some users choose to use webcam videos on their namahousou, but most users just use a still picture or a black screen. A namahousou where the user shows their face is known as "Kaodashi" (顔出し). Odorites will usually be streaming their dance practices through their Namahousou's
Nihongo de OK (日本語でおｋ) = implies that one should only talk in Japanese.
Points = (abbreviated as pt) are used on Nico Nico Douga as a way to show appreciation for a video. Points cost money to buy, and any user can donate points to a video. After receiving the points, the video will be advertised. The more points a video has the more the video is advertised.
Upotsu (うぽつ/うｐ乙) = A term used on videos, short for "up otsukare" (うｐおつかれ), used for congratulating someone for an upload of a video.
Utaite (歌い手) = is a Japanese term for people who cover previously released songs and post them on Nico Nico Douga under the utattemita category. The term "utaite" is unique to Nico Nico Douga singers, making it different from "kashu" (歌手), which means "singer" in general. For a more thorough definition please visit the utaite article on the wiki. UtattemitaEdit
Utattemita (歌ってみた) = is a Japanese term which literally means "tried to sing". For a more thorough definition please visit the utattemita page.
w = the japanese equivalent of "lol". It comes from the word "warau" (笑う), which means "to smile/laugh". As with "lol", often times multiple "w" are used.
Warota (ワロタ) = is a term derived from the word "waratta" (笑った), basically meaning "I lol'd". Similar in meaning to wwww, except it is used when talking about something specific that made the user laugh. Another variation would be Wara Wara (ワラワラ/笑笑)