Final answer:
Prospective observational studies involve collecting data on events as they occur, which is often seen in cohort studies where subjects are followed over time.
Step-by-step explanation:
Prospective as it relates to observational studies means collecting data on events as they occur. In a cohort study, which is a type of observational study, a group of subjects is selected at the start of the study and is followed over time, with data being collected periodically for months or even years into the future. Cohort studies allow researchers to establish a sequence and potentially draw causal inferences between exposure and outcome. In medicine, this is fundamental for understanding disease progression, treatment outcomes, and various health-related events as they naturally unfold.