The trombone is an instrument of the brass family, characterized by its traditional slide mechanism that allows for continuous variations of the length of the instrument (in contrast with the valve system employed by trumpets or horns). The word trombone derives from the Italian, and basically means 'large trumpet'. The trombone is a family of instruments of which the most popular are the tenor trombone and the bass trombone. Of these, the most frequently used is the tenor trombone, which is pitched in B flat and written in bass clef or alto clef, depending on the passage.