The term “serenade” is used to refer to several different kinds of musical composition, from an intimate song composed for a lover to an orchestral piece. Many English speakers use the term to refer to a song which is composed and performed for a lover, visualizing a musician standing under a loved one's window and singing a song in the evening hours. Many people have romantic associations with this form of serenade, understandably, since it implies a great deal of devotion on the part of the musician involved.
The love serenade also appears to be the oldest form of the serenade, and it seems to have arisen during the medieval era. Ideally, when someone is serenaded, the musician also composes the piece, and accompanies it with an instrument such as a guitar. Modern musicians may choose to play pieces which are composed by others, while people who lack musical ability sometimes try to get into the spirit of things by hiring musicians or bringing a stereo to play a piece of favored music.
In this sense, a serenade is a piece of music which is intended to honor someone and to celebrate love. Some people find such vocal and public displays of love a bit embarrassing, but others greatly enjoy them; if you are thinking of serenading someone, you may want to do some research on the sly to make sure that your performance will be well received. When playing a piece of your own composition, you can also add more depth of feeling to the song, personalizing it for the person you sing it for.
During the Baroque era, musicians began to compose pieces designed for a few instruments and meant to be performed outdoors. Many also included singers, and featured instruments which can be overpowering indoors, such as brass instruments. Baroque serenades included several movements, and sometimes they were staged, telling a story through the music in a style similar to opera.
In classical music, a serenade is a piece of light music composed for a full orchestra and meant to be performed indoors. Like Baroque serenades, the classical serenade contains several movements, and this musical form grew quite popular in Germany. Among many others, Mozart wrote a number of serenades which continue to be performed today.