One usage refers to a variety of a language that is a characteristic of a particular group of the language's speakers. Under this definition, the dialects or varieties of a particular language are closely related and, despite their differences, are most often largely mutually intelligible, especially if close to one another on the dialect continuum. The term is applied most often to regional speech patterns, but a dialect may also be defined by other factors, such as social class or ethnicity. 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 an ethnolect, and a geographical/regional dialect may be termed a regiolect (alternative terms include 'regionalect', 'geolect', and 'topolect'). According to this definition, any variety of a given language constitutes "a dialect", including any standard varieties. In this case, the distinction between the "standard language" (i.e. the "standard" dialect of a particular language) and the "nonstandard" dialects of the same language is often arbitrary and based on social, political, cultural, or historical considerations. In a similar way, the definitions of the terms "language" and "dialect" may overlap and are often subject to debate, with the differentiation between the two classifications often grounded in arbitrary and/or sociopolitical motives.
The other usage of the term "dialect", often deployed in colloquial settings, refers (often somewhat pejoratively) to a language that is socially subordinated to a regional or national standard language, often historically cognate or genetically related to the standard language, but not actually derived from the standard language. In other words, it is not an actual variety of the "standard language" or dominant language, but rather a separate, independently evolved but often distantly related language. In this sense, unlike in the first usage, the standard language would not itself be considered a "dialect", as it is the dominant language in a particular state or region, whether in terms of linguistic prestige, social or political status, official status, predominance or prevalence, or all of the above. Meanwhile, under this usage, the "dialects" subordinate to the standard language are generally not variations on the standard language but rather separate (but often loosely related) languages in and of themselves. Thus, these "dialects" are not dialects or varieties of a particular language in the same sense as in the first usage; though they may share roots in the same family or subfamily as the standard language and may even, to varying degrees, share some mutual intelligibility with the standard language, they often did not evolve closely with the standard language or within the same linguistic subgroup or speech community as the standard language and instead may better fit various parties’ criteria for a separate language.
For example, most of the various regional Romancelanguages of Italy, often colloquially referred to as Italian "dialects", are, in fact, not actually derived from modern standard Italian, but rather evolved from Vulgar Latin separately and individually from one another and independently of standard Italian, long prior to the diffusion of a national standardized language throughout what is now Italy. These various Latin-derived regional languages are, therefore, in a linguistic sense, not truly "dialects" or varieties of the standard Italian language, but are instead better defined as their own separate languages. Conversely, with the spread of standard Italian throughout Italy in the 20th century, regional versions or varieties of standard Italian have developed, generally as a mix of national standard Italian with a substratum of local regional languages and local accents. While "dialect" levelling has increased the number of standard Italian speakers and decreased the number of speakers of other languages native to Italy, Italians in different regions have developed variations of standard Italian particular to their region. These variations on standard Italian, known as regional Italian, would thus more appropriately be called "dialects" in accordance with the first linguistic definition of "dialect", as they are in fact derived partially or mostly from standard Italian.
A dialect is distinguished by its vocabulary, grammar, and pronunciation (phonology, including prosody). Where a distinction can be made only in terms of pronunciation (including prosody, or just prosody itself), the term accent may be preferred over dialect. Other types of speech varieties include jargons, which are characterized by differences in lexicon (vocabulary); slang; patois; pidgins; and argots. The particular speech patterns used by an individual are termed an idiolect.
A standard dialect (also known as a "standardized dialect" or "standard language") is a dialect that is supported by institutions. Such institutional support may include government recognition or designation; presentation as being the "correct" form of a language in schools; published grammars, dictionaries, and textbooks that set forth a normative spoken and written form; and an extensive formal literature that employs that variety (prose, poetry, non-fiction, etc.). There may be multiple standard dialects associated with a single language. For example, Standard American English, Standard British English, Standard Canadian English, Standard Indian English, Standard Australian English, and Standard Philippine English may all be said to be standard dialects of the English language.