Cantonese

A language spoken a lot in the south of China as well as around the world (especially in Chinese takeaways). It's roughly as related to Mandarin Chinese as English is to German: A speaker of (only) Cantonese cannot readily understand a speaker of (only) Mandarin Chinese and vice versa. Cantonese is spoken and not written, just as Mandarin Chinese is: Cantonese speakers and Mandarin Chinese speakers write in Written Chinese. It just happens that Mandarin Chinese is closer to the written standard. If you're from the US or the UK, when you think you hear "Chinese", it's likely Cantonese, especially if your knowledge of "Chinese" is limited to "chicken chow mein".