Speaking in tongues can have two distinct, but related, meanings. The first would be someone who is empowered by the Holy Spirit to speak in a recognizable foreign language in which the speaker has not previously been fluent. The second meaning would be someone who utters sounds not recognizable as a known foreign language, which is referred to by the term "glossolalia" and often described as babbling or gibberish.
I personally believe that the speaking in tongues on the day of Pentecost as described in the second chapter of the book of Acts was in the first category. Speaking in tongues as discussed by St. Paul in the first book of Corinthians, and elsewhere, may have fallen into the second category, but this is not entirely clear to me.
I also am a "cessationist," which means I believe that the "gift of tongues" ceased along with the passing of the apostolic period of first-century Christianity. I freely admit, though, that I may be wrong in this opinion, and I am not critical of my Christian brothers and sisters of charismatic persuasion who happen to believe otherwise.