These languages all share the fact that their writing systems are based partly or entirely on Chinese characters -- Hanzi in Chinese, Kanji in Japanese, and Hanja in Korean. Chinese requires between 4000 characters for a basic vocabulary to 40,000 characters for reasonably complete coverage. Whereas Japanese and Korean use fewer characters -- complete literacy in Japan can be expected with 2000 characters -- idiosyncratic use of Chinese characters in proper names requires many more. This number of characters cannot fit in the 256-character code space of 8-bit encodings, and therefore requires at least a 16-bit fixed width character encoding or multi-byte variable-length encodings.
CJK character encodings include:Unicode code space. There is much controversy among experts of Chinese characters about the desirability and technical merit of the "Han unification" process used to map multiple Chinese and Japanese characters sets into a single set of unified glyphs.
The term CJKV is used to mean CJK plus Vietnamese, which used Chinese characters prior to adopting a written language solely on Romanization.