TIL: "Winston W. Royce's final model, his intended improvement upon his initial "waterfall model", illustrated that feedback could (should, and often would) lead from code testing to design (as testing of code uncovered flaws in the design) and from design back to requirements specification (as design problems may necessitate the removal of conflicting or otherwise unsatisfiable / undesignable requirements)"

https://en.wikipedia.org/wiki/Waterfall_model#Modified_water...

Interesting because that's definitely not what's taught in the handful of Software Engineering books I've read, and steps backward are not canon (rather, they're called something besides Waterfall i.e Spiral or Iterative).

Looking at that page again, it looks like what I describe is called "pure waterfall".