“Singer-songwriter” is a tricky term because its literal meaning is different from its applied meaning. In a literal sense, a singer-songwriter is any artist who performs his or her own compositions. But most people who write and talk about music don’t use the label that way. They wouldn’t call Mick Jagger, Ozzy Osbourne or Prince a singer-songwriter, even though they all sing their own songs.
Most folks use the phrase to describe artists who make their lyrics the focus of a song, with the rhythm and instrumental arrangements relegated to a supporting role. Those supplementary materials can be ambitious and powerful (as on Paul Simon Graceland), or rudimentary and functional (as on John Prine’s debut), but in either case, the lyrics clearly lead the way. The term tells us nothing about the quality of the lyrics or music, but it does describe the sonic balance in the arrangement and the investment in the words.