Vernacular refers to the native language of a country or locality. In general linguistics, it is used to describe local languages as opposed to linguae francae, official standards or global languages. It is sometimes applied to nonstandard dialects of a global language.
For instance: in Western Europe up until the 17th century, most scholarly work was written in Latin, so works written in a native language (such as Italian or German) were said to be in the vernacular.
The vernacular is also often contrasted with a liturgical language (in Linguistics, the relationship between these "High" and "Low" languages or varieties of a language is referred to as diglossia). For example, until the 1960s, Latin Rite Roman Catholics held masses in Latin rather than in local vernacular language, to this day the Coptic Church holds liturgies in Coptic; though parts of mass are read in Amharic, the Ethiopian Orthodox Church holds liturgies in Ge'ez, etc. The Reformation was spread by the publication of Bibles and other religious writings in the vernacular, and the reforms of the Second Vatican Council permitted the use of vernacular liturgies in Roman Catholicism.
Similarly, in Hindu culture, traditionally religious or scholarly works were written in Sanskrit long after its use as a spoken language. With the rise of the bhakti movement from the 1100s onwards, religious works started being created in Tamil, Hindi, Kannada, Telugu and many other Indian languages throughout the different regions of India. For example, the Ramayana, one of Hinduism's sacred epics in Sanskrit had vernacular versions such as Ramacharitamanasa, a Hindi version of the Ramayana by the 16th century poet Tulsidas, and Kambaramayanam in Tamil by the poet Kamban.