Flash drought is a type of drought characterized by rapid intensification within a few weeks.It could be a "new normal" of drought in a warming climate,which needs further investigation.Regarding the debate on flash drought definition,this paper emphasizes the importance of understanding the difference and connection between flash drought and conventional drought,and clarifies flash drought in terms of rapid onset,duration,onset and recovery processes.This paper points out that the typical time scale of flash drought is sub-seasonal scale,which should be included in multi-scale drought system.This paper also overviews the progresses in extreme case diagnosis,detection and attribution of human activity,and ecological and environmental impact.Future focus could be the flash drought mechanism,including internal variability and external forcing,the interaction between flash drought and ecosystem,the identification of predictability sources of flash drought,and the development of prediction methods.It is encouraged to use research methods of earth system science and to develop advanced monitoring and modeling techniques for adapting to the increasing flash drought risk from a global change perspective.