The term has its origin in the Italian word “barca” meaning “boat” So a “barcarola” (alternatively “barcaruola”) became the name of a traditional folk song sung by Venetian gondoliers.

From this, the more widely used French form “barcarolle” developed in 18th and 19th century music. It was used for a piece of music composed in the style of the original Venetian “barcarola”. In classical music, some of the most famous barcarolles are Jacques Offenbach's "Belle nuit, ô nuit d'amour", from his opera “The Tales of Hoffmann”, Frédéric Chopin's Barcarolle in F-sharp major for solo piano, the three "Venetian Gondola Songs" from Mendelssohn's "Songs Without Words”, and Camille Saint-Saëns's Barcarolle in F major.

A barcarolle is characterised by a rhythm supposedly reminiscent of the gondolier's stroke, almost always in a 6/8 time signature at a moderate tempo.

More Info: en.wikipedia.org