scrum is themed off incremental development.
you build the core functionality and get something working, and then grow it. This allows you to deliver (possibly, just to testers) a partial product for evaluation with the understanding that there is 'more to come' but that the parts that were given over are nearly complete (may change a little after testing/ sign-off/ feedback). Its also about delivering the increments rapidly and consistently, with the most important features coming first, and 'extras' coming in last.
rapid prototyping means building a full interface first, with demonstrable functionality for most of the pieces of the interface that show 'how it will look and behave more or less'. Its building a near complete demo up front, which is nice for making a video / advertisement/etc even if the 'work' has not even really started yet. The idea has morphed over the decades to allow for using it as a way to produce products, but it was initially designed as a quick way to show the customer what they would be getting so any misconceptions were identified early.