Chinese (汉语/漢語; Hànyǔ or 中文; Zhōngwén) is a group of related, but in many cases mutually unintelligible, language varieties, forming a branch of the Sino-Tibetan language family. Chinese is spoken by the Han majority and many other ethnic groups in China.
Mandarin is the most common language in the world as it is the official language of Mainland China, Taiwan, and one of the official languages of Singapore. Thus, Mandarin is commonly referred to as “Chinese.”
But in fact, it is just one of many Chinese languages. China is an old and vast country geographically speaking, and the many mountain ranges, rivers, and deserts create natural regional borders.
Overtime, each region has developed its own spoken language. Depending on the region, Chinese people also speak Wu, Hunanese, Jiangxinese, Hakka, Yue (including Cantonese-Taishanese), Ping, Shaojiang, Min, and many other languages. Even in one province, there can be multiple languages spoken. For example, in Fujian province, you can hear Min, Fuzhounese, and Mandarin being spoken, each being very distinct from the other.