What characteristic distinguishes a ballad from other types of narrative poems?

Narrative poem is simply a type of poem that tells a story. There are several forms of narrative poems, it includes the idyll, epic, lay and of course the ballad. The ballad is different from the other forms of narrative poems because it has a rhyme and is delivered through singing. The dramatic story is delivered in details unlike the others that are simply describing to the reader what happened in the story. Ballads are usually written in a quatrains which means there are four lines in a stanza with the "abcb" rhyme.