The T–V distinction is the contextual use of different pronouns that exists in some languages and serves to convey formality or familiarity. Its name comes from the Latin pronouns tu and vos. The distinction takes a number of forms and indicates varying levels of politeness, familiarity, courtesy, age or even insult toward the addressee. The field that studies and describes this phenomenon is sociolinguistics.

Many languages lack this type of distinction, instead relying on other morphological or discourse features to convey formality. English historically contained the distinction, using the pronouns thou and you, but the familiar thou largely disappeared from the era of Early Modern English onward, with the exception of a few dialects. Additionally, British commoners historically spoke to nobility and royalty using the third person rather than the second person, a practice that has fallen out of favour. English speakers today often employ semantic analogues to convey the mentioned attitudes towards the addressee, such as whether to address someone by given name or surname or whether to use sir or madam. Under a broader classification, T and V forms are examples of honorifics.

The T–V distinction is expressed in a variety of forms. Two particularly common means are:

• Addressing a single individual using the second-person plural forms in the language, instead of the singular (e.g. in French).
• Addressing individuals with another pronoun with its own verb conjugations (e.g. in Spanish).