Pali is a middle Indo-Aryan dialect or prakrit. It is most famous as the language in which the scriptures of Theravada Buddhism (also known as the Pali Canon or in Pali the Tipitaka) were written down in Sri Lanka in the first century BC. Pali has been written in a variety of scripts, from Brahmi, Devanagari and other Indic scripts. The word Pali itself signifies "line" or "(canonical) text" and it is now classified as a literary language.

While it is uncertain whether Pali was ever a spoken language in the sense of a language people use to communicate with each other, Pali has long been the language in which Theravada Buddhists chant. It is widely believed that Gotama Buddha spoke either in the vernacular Magadhi or some other middle Indo-Aryan vernacular which was the language of the people near Benares in North-East Central India (now Varanasi) where he resided and taught. Pali was considered by early Buddhists to be linguistically similar to old Magadhi or even a direct continuation of that language. However, Magadhi is an Eastern Indian language whereas Pali most closely resembles Western Indian inscriptions.

Today Pali is studied mainly to gain access to Buddhist scriptures, and is frequently chanted. The Pali Text Society, based in the United Kingdom, has since its founding in 1881 been a major force in promoting the study of Pali by Western scholars. The society publishes these scriptures in romanised Pali and most of them in English translation as well.

Many Pali words come from Sanskrit with the original meaning slightly altered to accommodate the content of Buddhism. Other Pali words come from places where Pali was used (e.g. Sri Lankans adding Sinhalese words to Pali.)

The Pali vocabulary reflects the fact that Pali is used principally to convey the teachings of the Buddha. Similar words in Sanskrit can have slightly different meanings than those of Pali. For example, Buddhists do not believe things have an essential nature or eternal soul, so the literal meaning of the word "dhamma" (Sanskrit "dharma") is modified to reflect this.

The philosophy of Sanskrit and Pali are opposites and reflect the division between Buddhism and the Brahmanical thought of the Middle Indic period. While Sanskrit words were thought to inhere as a part of the thing they described, Pali words were thought to have only conventional significance.