Glossolalia is fabricated, meaningless speech.
According to Dr. William T. Samarin, professor of anthropology and linguistics at the University of Toronto,
glossolalia consists of strings of meaningless syllables made up of sounds taken from those familiar to the speaker and put together more or less haphazardly .... Glossolalia is language-like because the speaker unconsciously wants it to be language-like. Yet in spite of superficial similarities, glossolalia fundamentally is not language [Nickell, 108].
When spoken by schizophrenics, glossolalia are recognized as gibberish. In charismatic Christian communities glossolalia is sacred and referred to as "speaking in tongues" or having "the gift of tongues." In Acts of the Apostles, tongues of fire are described as alighting on the Apostles, filling them with the Holy Spirit. Allegedly, this allowed the Apostles to speak in their own language but be understood by foreigners from several nations. Glossolalics, on the other hand, speak in a foreign language and are understood by nobody.
Glossolalics behave in various ways, depending upon the social expectations of their community. Some go into convulsions or lose consciousness; others are less dramatic. Some seem to go into a trance; some claim to have amnesia of their speaking in tongues. All believe they are possessed by the Holy Spirit and the gibberish they utter is meaningful. However, only one with faith and the gift of interpretation is capable of figuring out the meaning of the meaningless utterances. Of course, this belief gives the interpreter unchecked leeway in "translating" the meaningless utterances. Nicholas Spanos notes: "Typically, the interpretation supports the central tenets of the religious community" [Spanos, 147].
Uttering gibberish that is interpreted as profound mystical insight by holy men is an ancient practice. In Greece, even the priest of Apollo, god of light, engaged in prophetic babbling. The ancient Israelites did it. So did the Jansenists, the Quakers, the Methodists, and the Shakers.