地方语言（简称方言）最简单的定义就是指一个特定地理区域中某种语言的变体。然而，值得注意的是，在对所谓的「语言」和「方言」进行定义时，无论是采用社会语言学者「相互理解性」的判别标准，或者是历史语言学者「历史发展关系」的判别标准，我们都无可避免会碰到准则上相当程度的任意和困难。因此，多数人同意，实际操作上，判别语言和方言的标准往往是政治性的，如果某种语言完成标准化（特别是书面标准化）的进程，我们通常将其称之为「语言」(其本质上可以被视为是一种「标准化方言」)；如果某种语言没有完成这个进程，则我们通常将其称为「方言」（本质上可以被视为是一种「非标准化方言」）。

The term dialect (from Latin dialectus, dialectos, from the ancient Greek word διάλεκτος diálektos, "discourse", from διά diá, "through" and λέγω legō, "I speak") is used in two distinct ways to refer to two different types of linguistic phenomena.

One usage—the more common among linguists—refers to a variety of a language that is a characteristic of a particular group of the language's speakers. The term is applied most often to regional speech patterns, but a dialect may also be defined by other factors, such as social class. A dialect that is associated with a particular social class can be termed a sociolect, a dialect that is associated with a particular ethnic group can be termed as ethnolect, and a regional dialect may be termed a regiolect. According to this definition, any variety of a language constitutes "a dialect", including any standard varieties.