This song got its name from the actress Rosanna Arquette, who was dating Toto keyboard player Steve Porcaro at the time. Porcaro didn't write the song - it was written by Toto leader David Paich, who was always looking for good ideas for lyrics.
In a Songfacts interview with Paich
, he explained: "'Rosanna' was about a high school love, one of my first loves, but I just tagged another Rosanna's name on there because she was going at the time with Steve Porcaro, my best friend. He had just met her and was looking to title a song with her name, and it just fit perfectly for that song right there. So it's got her name on it, but it's really about another high school sweetheart, which is how songs happen sometimes."