The American writer Sylvia Wright coined the term mondegreen in an essay "The Death of Lady Mondegreen," which was published in Harper's Magazine in November 1954. In the essay, Wright described how, as a young girl, she misheard the final line of the first stanza from the 17th century ballad "The Bonnie Earl O' Murray." She wrote:
When I was a child, my mother used to read aloud to me from Percy's Reliques, and one of my favorite poems began, as I remember:
Ye Highlands and ye Lowlands,
Oh, where hae ye been?
They hae slain the Earl Amurray,
And Lady Mondegreen.
The actual fourth line is "And laid him on the green." As Wright explained the need for a new term, "The point about what I shall hereafter call mondegreens, since no one else has thought up a word for them, is that they are better than the original."
Source: Wikipedia