Sociolinguistics is a hybrid of sociology and linguistics. It is the study of the relationship between language and society. The language we use is influenced by social contexts. This is true, for example, in the use of accents. Sociolinguistics is a very broad field.
According to Scott Thornbury, sociolinguistics was important to the rise of the communicative approach and the functional syllabus. The communicative approach to teaching languages became popular in the late twentieth century. A functional syllabus includes the appropriate language for: greeting people, asking for information, making requests, etc. There are, for instance, many ways to make a request ("Can you . . .?," "Would you mind . . .?," etc.), and the correct way depends on the situation, age, and relationship of the speakers. Japanese, for example, has a complicated system of language forms used based on these factors.
Another aspect of sociolinguistics is bilingualism. Children use their first and second language in bilingual schools. Over 70% of the world's population is bilingual or multilingual.
Of the many subtypes of the study of linguistics – the study and description of word formation (as inflection, derivation, and compounding) in language, the most relevant to current social inquiries is sociolinguistics – looking at how language uses vary with reference to social classes, geography, and political orientations – gender differences, occupations, bilingualism, etc. When we speak of accents (high-class, Brooklyn, Southern, “foreign,” etc.) we are referring to sociolinguistic variation from what might be called “standard English” pronunciation and use. But the term itself is socially suspect, putting some make-believe standards in place that have very little “authority” to a claim of superiority. Besides “pronunciations,” there are also variations in the use of suffixes, prefixes, and other word parts – we may not think the Southern uses “you all” or “y’all” are “proper” language elements, for example. Studying these linguistic variations – their derivation, their localizations, their legitimacy in formal discourse, their identification signature, etc., is the province of those sociolinguists specializing in this subset of the more general study of morphology in language.