Adding to @srg36, De Novo means an application sent by the medical device sponsor to FDA. So it establishes a new “device type” along with classification, regulation, necessary controls and product code, and it is eligible to serve as a predicate for new medical devices, where appropriate 510k process. So instead of going through 510k process there is 2 alternative pathways: 510k to de novo, where you attempt 510k route with proposed predicate device and submission found NSE, but candidate for de novo; or direct de novo, it is useful if you believe proposed device is viable de novo candidate. During the 510k to de novo, sponsor submits 510k, FDA reviews 510k submission and makes NSE finding due to lack of predicate, then sponsor submits de novo application, finally FDS reviews de novo application. On the other hand, during direct de novo, sponsor submits de novo application, then FDA reviews it.
In my opinion, this makes much more sense. It saves time for the companies that have an important product that needs to be released. So now companies don’t have to wait for the 510K and just skips right to the de novo application.