This is the official standard test used in Mainland China for Chinese proficiency level. Taking this exam is essential to applying to overseas programs in China that are conducted in Mandarin. In 2021, the format of the HSK has was revised include many more words, and to include nine levels instead of six, so many online test preparation materials still go by the format of the old exams.
There are also Chinese language tests used in China. HSKK (汉语水平口语考试) is the standard speaking test, and there are also proficiency tests for business and medical Chinese. More information about them can be found on the official testing website.
This is the standard test used for university and job entry in Taiwan.