Speaking in tongues, also known as glossolalia, is an activity or practice in which people utter words or speech-like sounds, often thought by believers to be languages unknown to the speaker. One definition used by linguists is the fluid vocalizing of speech-like syllables that lack any readily comprehended meaning. In some cases, as part of religious practice, some believe it to be a divine language unknown to the speaker. Glossolalia is practiced in Pentecostal and charismatic Christianity, as well as in other religions.

Pentecostalism or classical Pentecostalism is a Protestant Charismatic Christian movement that emphasizes direct personal experience of God through baptism with the Holy Spirit. The term Pentecostal is derived from Pentecost, an event that commemorates the descent of the Holy Spirit upon the Apostles and other followers of Jesus Christ while they were in Jerusalem celebrating the Feast of Weeks, as described in the Acts of the Apostles.