A song is a musical composition with vocals. It may be sung with or without instrumental accompaniment (a cappella), by solo singers or with a choir. It can contain lyrics and music that tell a story or are highly personal, or the words can be unrelated to the musical accompaniment. The style can be folk, pop, rock, rap, or classical. Songs can be in a major or minor key. They can follow a particular formula such as verse-chorus-verse, or they can be written as a riff, ad lib, strophe or ballad.
There are no set rules for whether the music or lyrics come first, as long as they work well together. The most important thing is that the songwriter writes and records something that they are happy with. It is also good to make notes of any ideas you have while they are fresh in your mind, even if it is just a quick recording on your phone or scribbled on a piece of paper, as there is nothing worse than forgetting an idea that you really wanted to use.
The earliest known written songs are romances, love songs to an ideal or imaginary person and religious songs. Later, a tradition of writing poetic or prose lyrics to composed music developed, with troubadours and bards in Europe and Elizabethan lutenists in England. These are known as art songs, and the modern form of popular song evolved from them. Art songs typically have elaborate, sophisticated accompaniments that underpin, illustrate or contrast with the voice.