It was a slang word for the secret or cant language used by beggars, thieves, Roma people, etc., hence the fluent plausible talk that a cheap-jack employs to pass off his goods. Many illusionists, e.g., card magicians use patter both to enhance the show and to distract the attention of the spectators.
It is thus used of any rapid manner of talking, and of a patter-song, in which a very large number of words have to be sung at high speed to fit them to the music. A western square dance caller may interpolate patter — in the form of metrical lines, often of nonsense — to fill in between commands to the dancers.
The word, though in some of its senses affected by "patter", to make a series of rapid strokes or pats, as of raindrops, is derived from the way of quick and mechanical mumbling of prayers and is the colloquial shortening of "Pater Noster".
In hypnotherapy, the hypnotist uses a 'patter' or script to deliver positive suggestions for change to the client.