In music, a serenade (or sometimes serenata) is, in its most general sense, a musical composition, and/or performance, in someone's honor. There are three general categories of serenade in music history.
1) In the oldest usage, which survives in informal form to the present day, a serenade is a composition performed for a lover, friend, or other person to be honored, typically in the evening and often below a window. The custom of serenading in this manner began in the Medieval era or Renaissance, and the word "serenade" as commonly used in current English is related to this custom. Music performed followed no one particular form, except that it was typically sung by one person accompanying himself on a portable instrument, for example a guitar or an accordion. Works of this type also appeared in later eras, but usually in a context that referred specifically to a past time, such as an arias in an opera (there is a famous example in Mozart's Don Giovanni).
2) In the Baroque era, and generally called a Serenata (Italian "serenade"--since this form occurred most frequently in Italy), a serenade was a type of cantata performed outdoors, in the evening, with mixed vocal and instrumental forces. Some composers of this type of serenade include Alessandro Stradella, Alessandro Scarlatti, Johann Joseph Fux, Johann Mattheson, and Antonio Caldara. Usually these were large-scale works performed with minimal staging, intermediate between a cantata and an opera. According to some commentators, the main difference between a cantata and a serenata, around 1700, was that the serenata was performed outdoors and therefore could use instruments which would be too loud in a small room--for example trumpets, horns and drums.
3) The most important and prevalent type of serenade in music history is a work for large instrumental ensemble in multiple movements, related to the divertimento, and mainly being composed in the Classical and Romantic periods, though a few examples exist from the 20th century. Usually the character of the work is lighter than other multiple-movement works for large ensemble (for example the symphony), with tunefulness being more important than thematic development or dramatic intensity. Most of these works are from Italy, Germany, Austria and Bohemia.
The most famous examples of the serenade from the 18th century are undoubtedly the ones by Mozart, which are works in more than four movements, and sometimes as many as ten. The most typical ensemble for a serenade was a wind ensemble augmented with basses and violas: instrumentalists who could stand, since the works were often performed outdoors. Frequently the serenades began and ended with movements of a marchlike character--since the instrumentalists often had to march to and from the place of performance. Famous serenades by Mozart include the Haffner Serenade and one of his most famous works, Eine Kleine Nachtmusik, which is atypical for only containing string instruments.
By the 19th century, the serenade had transformed into a concert work, less associated with outdoor performance for honorary occasions, and composers began to write serenades for other ensembles. The two serenades by Brahms are rather like light symphonies, except that they use an ensemble Mozart would have recognized: a small orchestra (in the case of the Serenade No.2, an orchestra entirely without violins). Dvořák, Tchaikovsky, Josef Suk and others wrote serenades for strings only, as did Hugo Wolf, who wrote one for string quartet (the Italian Serenade). Other composers to write serenades in a Romantic style include Richard Strauss, Max Reger, Edward Elgar and Jean Sibelius.
Some examples of serenades in the 20th century include the Serenade for Tenor, Horn and Strings by Benjamin Britten, the Serenade for piano by Stravinsky, Serenade for baritone and septet Op. 24 by Arnold Schoenberg, and the movement entitled "Serenade" in Shostakovich's last string quartet, No. 15 (1974).
A Latin America example of the serenata, or serenade can be found here: http://www.theserenata.com