The post-traumatic stress disorder (PTSD) diagnosis encompasses heterogeneous presentations, many of the diagnostic criteria are not trauma-related and almost all PTSD symptoms are common to several psychiatric diagnoses. Flashbacks are the only symptom unique to PSTD. However, the absence of a consensus definition of flashbacks means that this term means different things to different people, causing misunderstanding and miscommunication, and presumably affecting treatment. This Refreshment discusses how flashbacks are defined in DSM-5-TR and ICD-11 (essentially, as reliving/re-experiencing when awake) and briefly describes the dual representation theory's account of flashbacks. In discussing what flashbacks are and are not, it aims to promote improved understanding, assessment and diagnosis of PTSDs.