The definition of 'Purple Rain'

"The emotional lyrics have multiple meanings; on the surface, they seem to be an apology from one lover to another, though on a deeper level, they become more of a spiritual allegory. It is a theory that "Purple Rain" is a metaphor for heaven, inspired by the testimonies of a woman who died on the operating table that the afterlife is full of falling purple rain."

Extracted from Wikipedia:

http://en.wikipedia.org/wiki/Purple_Rain_%28song%29