As mean sea level rise (MSLR) accelerates, it will become increasingly necessary and useful to distinguish coastal “flooding” from “inundation.” The growing number of coastal MSLR vulnerability assessments makes it clear that confused usage is abundant. We propose that the term “flooding” be used when dry areas become wet temporarily—either periodically or episodically—and that “inundation” be used to denote the process of a dry area being permanently drowned or submerged. According to these proposed defnitions, flooding is always higher than inundation, but they are fundamentally different. Flooding, including tidal flooding, is and has been dominant along open coasts. However, inundation is likely to become ever more important in the coming decades and centuries and may itself eventually become a dominant physical coastal process. Differentiating between the two will clarify and emphasize the differences between these processes.