"Longitudinal" refers to a type of study or research that collects data over an extended period. This approach allows researchers to observe changes and developments in the same subjects, such as individuals or groups, over time. It is commonly used in fields like psychology, sociology, and medicine to track progress or trends. In contrast to cross-sectional studies, which analyze data at a single point in time, longitudinal studies provide a more comprehensive view of how variables interact and evolve. This method can reveal patterns and causal relationships that might not be evident in shorter studies, making it valuable for understanding complex issues.