In music, a glissando, also known as a gliss, is a musical composition tool and playing technique that sounds like a smooth slide from one note to another. On paper, it looks like a squiggly line leading from the starting note to the note the slide should end on. The plural form of glissando is glissandi. One well-known appearance of the gliss is in George Gershwin's "Rhapsody in Blue," which features a clarinet sliding up to the first sustained note of the piece. The instrument best known for its sliding notes is the trombone, which uses a set of sliding tubes to move the instrument smoothly from note to note.
It usually comes in two forms: continuous and discrete, which can also be known as chromatic. The continuous form is a smooth slide through notes that is played on an instrument that can move from note to note without stopping on the notes in between. Instruments that can play a continuous gliss include trombone, theremin, or unfretted string instruments like violins. Some woodwind and brass instruments can also play a nearly continuous glissando with special use of the embouchure, or mouth position, to bend the notes.
Discrete or chromatic glissandi have distinct note changes that occur quickly, but with audible note divisions within the glissando. This type of gliss is generally used not because the slide is not meant to be smooth, but because the mechanics of the instrument prevent playing a smooth slide. When written in musical notation, it looks the same as a continuous gliss, and the instrumentalist is intended to assume that the slide should be played as smoothly as the instrument allows. The frets on the neck of a string instrument cause the string to stop on different notes, so a glissando on a fretted instrument would be a discrete glissando. Most people are familiar with this type of gliss from piano slides likes the ones heard in "Great Balls of Fire" by Jerry Lee Lewis.
A similar technique called the portamento also involves bending or sliding the transition between notes. Many people consider the portamento to be the same thing as a glissando, while others believe that a portamento exists when sliding between two notes, and a glissando is a magnanimous slide that moves through several different notes. Other composers feel that the portamento is the sliding between two notes that occurs in each note movement of a gliss. Generally, the portamento is used more frequently in vocal music, while a gliss is more commonly seen in instrumental music, particularly jazz.