This character encoding method is used to code for Simplified Chinese characters, which are used in Mainland China and Singapore. Taiwan and Hong Kong, which use Traditional Chinese characters, have Big5 as their standard.
Like ANSI, GB standards fall in many areas. In computer contexts, "GB" alone is often used to mention GB 2312-1980 issued in 1980, or GB 18030-2000 issued in 2000. These two are encoding standards for encoding Chinese characters.
There are about 7200 characters in the GB codeset, versus approx. 16000 in the Big-5 codeset. The pinyin, romanization of these characters, is standardized as well. It can be used as one of the several Chinese input systems (e.g., by typing Z-H-O-N-G for the character 中)