The difference between the two is what happens after development
"Early on, software development didn't really fit under a particular management umbrella. Then along came waterfall, which spoke to the idea that software development could be defined by the length of time an application took to create or build.
Back then, it often took long periods of time to create, test, and deploy software because there were no checks and balances during the development process. The results were poor software quality with defects and bugs and unmet timelines. The focus was on long, drawn-out plans for software projects..."