Glossolalia (from Greek glossa γλώσσα "tongue, language" and lalô λαλώ "speak, speaking") is the practice of making unintelligible utterances, often as part of religious practices. Frederic William Farrar first used the word glossolalia in 1879.
Xenoglossy "the phenomenon of uttering intelligible words of a language unknown to the speaker" which some authors use interchangeably with glossolalia meaning "speak in tongues", while others use it to differentiate whether or not the utterances are intelligible as a natural language.
While occurrences of glossolalia are widespread and well documented, there is considerable debate within religious communities (principally Christian) and elsewhere as to both its status (the extent to which glossolalic utterances can be considered to form language), and its source (whether glossolalia is a natural, supernatural, or spiritual phenomenon).
The origin of the modern charismatic Christian concept of speaking in tongues is the miracle of Pentecost, recounted in the New Testament book of Acts, in which Jesus' apostles were said to be filled with the Holy Spirit and spoke in languages foreign to themselves, but which could be understood by members of the linguistically diverse audience.