Glossolalia, or Speaking in Tongues, is the practice of some religious people of uttering unintelligible, speech-like sounds, usually during periods of intense, ecstatic religious worship. The practice is most common among evangelical fundamentalist Christians, though it is not confined to Christian religions. In a way it is similar to the ululation practiced by some Muslims. The practice among Christians is derived from the books of Acts and I Corinthians in the Bible, though according to Acts the tongue-speaking of the apostles was actually Xenoglossy- the speaking of a natural language by someone previously unfamiliar with that language, as evidenced by the response of the listeners, who said, "Are not all these men who are speaking Galileans? Then how is it that each of us hears them in his own native language?" (Acts 2, 7-8). Since the Xenoglossy of the apostles was an immediate response to the action of the Holy Spirit at Pentecost, fundamentalists regard it as one of the chief signs of being "baptized in the Holy Spirit."
The practice among Christians was revived in modern times by preachers such as Kenneth Hagin and Kenneth Copeland in the mid-seventies as part of the "Pentecostal revival." Some, like Hagin, took the practice a step further by engaging in even stranger acts "under the influence of the Spirit." At one sermon, Mr. Hagin was speaking of being "drunk in the Spirit", when he suddenly started acting as though he were staggering drunk- laughing, slurring his words, and stumbling around the room, an action that the audience members immediately started mimicking. On other occasions, Mr. Hagin began hissing like a snake, after which the audience of course immediately started to also make animal sounds, with some lowing like cows, some barking, and some squealing like pigs.
Glossolalia is often described as a "prayer language" or "angelic language." It is said by many evangelicals that glossolalia can be used to pray when you're not quite sure what to pray, or when you wish to speak to God privately- ignoring the fact that if God is omniscient, he doesn't need prayer at all, let alone prayer in a "language" that even the believer does not understand. Some say that it is a language that Satan cannot understand. It is also interesting to note that if it is, indeed, an "angelic language", then angels are so advanced as to have no need of such complex languages as humans use, since most glossolalia seems to consist of the same half-dozen or so syllables repeated over and over again. "SH" and "LA" sounds seem to make up a majority of this "speech", with many extensively rolled "R"s thrown in.