popular  usually written using kana alone  noun  noun (generic)  Internet slang 

• mackerel (esp. the chub mackerel, Scomber japonicus)
• server (esp. in an online game)

popular  abbreviation  noun  noun (generic)  noun or participle taking the aux. verb する  Internet slang 

• copy-and-paste
• copypasta (block of text that is copied and pasted across the Internet)

popular  abbreviation  Internet slang  noun  noun (generic) 

• post (to a BBS), comment (on a blog)

popular  noun  noun (generic)  Internet slang 

• tree (esp. a Christmas tree)
• tree (structure, diagram, etc.)
• thread (on Twitter)

popular  な adjective  adjective (generic)  Internet slang  suffix 

• trendy, in, now
• currently at ..., now doing ..., in the middle of ...

popular  noun  noun (generic)  derogatory  Internet slang 

• pizza
• fat, ugly person

popular  prefix  な adjective  adjective (generic)  abbreviation  Internet slang  noun  noun (generic)  noun or participle taking the aux. verb する 

• multi-
• multi-post
• multi-level marketing, pyramid selling, chain referral

Internet slang  noun  noun (generic) 

• original poster (of an Internet thread), OP

noun  noun (generic)  Internet slang 

• halo
• paid dating (esp. with an underage girl; oft. involving selling of sex), compensated dating

gikun or jukujikun  obsolete reading  search-only kanji form  noun  noun (generic)  Internet slang 

• small fish, small fry
• (a) nobody, small fry, unimportant person
• noob, weak player