Despite agreement that snacks contribute significant energy to children's diets, evidence of the effects of snacks on health, especially in children, is weak. Some of the lack of consistent evidence may be due to a non-standardized definition of snacks. Understanding how caregivers of preschool-aged children conceptualize and define child snacks could provide valuable insights on epidemiological findings, targets for anticipatory guidance, and prevention efforts. Participants were 59 ethnically-diverse (White, Hispanic, and African American), low-income urban caregivers of children age 3–5 years. Each caregiver completed a 60–90 min semi-structured in-depth interview to elicit their definitions of child snacks. Data were coded by two trained coders using theoretically-guided emergent coding techniques to derive key dimensions of caregivers' child snack definitions. Five interrelated dimensions of a child snack definition were identified: (1) types of food, (2) portion size, (3) time, (4) location, and (5) purpose. Based on these dimensions, an empirically-derived definition of caregivers' perceptions of child snacks is offered: A small portion of food that is given in-between meals, frequently with an intention of reducing or preventing hunger until the next mealtime. These findings suggest interrelated dimensions that capture the types of foods and eating episodes that are defined as snacks. Child nutrition studies and interventions that include a focus on child snacks should consider using an a priori multi-dimensional definition of child snacks.