Definition of speaking in tongues:
(n) :
(Protestantism) The act of speaking a language one does not know, or speaking elaborate but apparently meaningless speech, while in a trance-like state (or, supposedly, under the influence of a deity or spirits); glossolalia.
(n) :
(Catholicism) The ability of speaking fluently a foreign language without prior learning or knowledge, supposedly under the influence of God; glossolalia.