In English, the word "dialect" is usually used interchangeably with "accents". We tend to think about people with different accents and slightly different vocabulary. However, dialects (方言) are very different from accents (口音). A majority of Chinese dialects are mutually unintelligible (can not be understood by each other). They not only have different vocabulary and pronunciation, but also different grammar and slang.
In the western world, we tend to think of dialects as variants or subgroups of a language. Naturally, this creates a hierarchy in which dialects are seen as lesser versions of a language. 方言, which is now translated as "dialect", but it seems that there is something to translation. 方 comes from 地方 meaning "place" and 言 comes from 語言 meaning "language". Putting this together, we can get: 地方的語言, or the language of a place. For a lot of Chinese history, 方言 did not refer to "dialects" but to the different vernacular languages across China. We tend to think of dialects as things that break off from a language, but for Chinese, we should reframe this perspective. What if the different dialects are what makes up a language?
In English, we do not distinguish the written and spoken forms of languages: "English" refers to both spoken and written English, "French" refers to both spoken and written French. However, Chinese makes the distinction between vernacular and written languages. You can either have the 文 suffix or the 語 suffix. The 文 suffix generally refers to the written language. On the other hand, the 語 suffix refers to the spoken language.* For example, 英文 refers to written English while 英語 refers to spoken English.
*In colloquial Chinese, the 文 suffix is used more generally, referring to both the spoken and written language. The opposite is not true for 語/話.
During the Qin Dynasty, Qin Shihuang (秦始皇) unified the written script in China. As a result, written Chinese (中文) has been standardized for thousands of years. However, spoken Chinese (中國話) has never been standardized until fairly recently. Of course, the central government has always had an official language (官話), but there was never an official spoken language for the entire country.
In Chinese, dialects are denoted with the 話 suffix; for example, Cantonese is 廣東話 (Guangdong Speech) and Hokkien is 福建話 (Fujian Speech). For the purposes of this website, I define what connects these dialects together as their writing system. People who read and write dialects use Chinese characters (漢字).
But even this definition of dialects is inconsistent. Is Japanese, which uses Chinese characters (Kanji, 漢字) a dialect of Chinese? What about Vietnamese, which used Chữ Nôm derived from Chinese characters? At what point do we draw the line between a language and a dialect?