The labels "retrospective" and "prospective" strongly connote study quality, often favouring prospective studies. However, three definitions of these terms exist, each suggesting distinct methodological limitations. In this review, we summarize and evaluate these definitions. Caution is warranted when labeling a study "retrospective": This label should only be used when implying a risk of recall bias, which can only occur in retrospective data collection. Generally, assessing random and systematic errors is necessary to appraise study quality rather than relying on ambiguous labels.