by Danlee Mitchell and Jack Logan, Ph.D.

Tempo (an Italian word) identifies the rate of speed of the beat of music and is measured by the number of beats per minute. There is a machine known by the term metronome which emits a steady short "click" or flash that may be adjusted to various rates of speed (tempi), thereby indicating at what speed (how fast or slow) a composition should proceed.
A beat may be slow or fast. Human perception perceives a range of tempo speed from about 30 to 240 beats per minute. "Romantic" songs tend to have a medium tempo, while dance music may range from slow to fast tempo. March music reflects a comfortable marching pace -- about 120 beats per minute. Faster tempi (plural of tempo) are more energizing while slower tempi are more soothing. Tempo is an important ingredient in the mood of any example of music, whether it be aggressive or calming in effect with excitement generally revealed through a fast tempo while solemnity is always revealed through a slow tempo.
In music terminology and notation tempo indications are most often expressed in the Italian language. The Italians were the first to develop written tempo and mood indications in music. Prior to 1600 tempo markings were practically unknown in music notation. One of the first composers to use modern tempo markings was the Italian composer Adriano Banchieri (1568-1634). During the mid-19th century composers began using their native language for tempo and mood indications as a political expression of the emerging nationalism of the period. In the 20th century tempo and mood indications are a mixture of Italian terms and the native language of the composer.
Tempo indications are of no particular interest to the average listener of music except that they are used to designate various movements of multi-movement works and are often used in the titles of compositions from the common practice period of music (1800 A. D. to the present).
Arranged below is a list of the basic Italian terms referring to tempi in music followed by the derivative forms of the basic terms, and the modifiers that add descriptive directions to the basic and derivative terms.
Italian Terms largo: very slow, broad, large lento: slow adagio: slow, comfortable, easy andante: moderately slow, a walking pace moderato: moderate allegro: fast, cheerful, joyful vivace: lively, quick presto: very fast, rapid
Derivative Terms larghetto: slightly slower than largo andantino: slightly slower than andante allegretto: slightly slower than allegro prestissimo: extremely fast, as fast as possible
Modifiers of Tempo agitato: agitated (e.g. Allegro agitato) animato: animated (e.g. Allegro animato) appassionato: passionately (e.g. Andante appassionato) assai: very (e.g. Allegro assai) cantabile: singing (e.g. Adagio cantabile) con brio: with spirit (e.g. Allegro con brio) con fuoco: with fire (e.g. Allegro con fuoco) con moto: with motion (e.g. Allegro con moto) espressivo: expressively (e.g. Adagio espressivo) grazioso: with grace (e.g. Andante grazioso) ma: but (e.g. Moderato, ma con brio) maestoso: majestically (e.g. Andante maestoso) marcato: marked, stressed (e.g. Andante marcato) molto: very, much (e.g. Molto allegro/Molto adagio) non: not (e.g. Allegro non troppo) non troppo: not too much (e.g. Allegro, ma non troppo) piu: more (e.g. Piu allegro) poco, un poco: little, a little (e.g. Poco adagio or Un poco piu adagio) sostenuto: sustained (e.g. Andante sostenuto, etc.)
At certain moments within a composition the beat may gradually speed up, slow down or be irregular. This happens most often in introductions at the beginning of pieces or during transition points within a piece. These tempo changes are expressed in Italian terms some examples of which are
accelerando: gradually becoming faster, ritard, ritardando: gradually becoming slower, rubato: a flexible tempo of slight accelerandos and ritardandos, fermata: a note that is sustained longer than its notated value.
All of the preceding terms are relative and approximate. Different musicians interpret them according to their personal tastes and moods. There is no definitively "correct" or "wrong" tempo for any musical piece; however, a tempo that is vastly far away from the "spirit" of the designated tempo will destroy the flow and cohesiveness of any musical composition.