As Beethoven used the term, a "bagatelle" is a little something for piano: A brief, entertaining piece. He published three sets of them, opus numbers 33, 119, & 126. These number 24 in all. In addition, there are a few which did not receive opus numbers, including the two named above, which now have "WoO" numbers, an abbreviation which means, simply, "work without opus number." Another popular bagatelle is called "Rage over a Lost Penny. In general, these are all diverting chips from Beethoven's work-bench.
Description by Joseph Stevenson