The topic of “Flash Drought” is rapidly gaining attention within both the research and drought management communities. This literature review aims to synthesize the research to-date and provide a basis for future research on the topic. Specifically, our review is focused on documenting the range of definitions of “flash drought” being proposed in the research community. We found that the term first appeared in the peer-reviewed literature in 2002, and by 2020 has become an area of active research. Within that 18-year span, “flash drought” has been given 29 general descriptions, and 20 papers have provided measurable, defining criteria used to distinguish a flash drought from other drought. Of these papers, 11 distinguish flash drought as a rapid-onset drought event while eight distinguish flash drought as a short-term or short-lived, yet severe, drought event and one paper considers flash drought as both a short-lived and rapid onset event. Of the papers that define a flash drought by its rate of onset, the rate proposed ranges from 5 days to 8 weeks. Currently, there is not a universally accepted definition or criteria for “flash drought,” despite recent research that has called for the research community to adopt the principle of rapid-intensification of drought conditions.