True eyeties say neither (“salsa” is the word used for most sauces in standard Italian, local dialects have a ton of other terms, including “ragu”). Never took time to find out why Italian Americans use the English word “gravy.”
It's not settled science! Here's a researched discussion:
Sauce or Gravy? The Secret, Fervent Debate at the Heart of the Italian American Spaghetti Dinner