Trajectory analysis is a methodological approach or research field dedicated to studying and characterizing the dynamic progression, path, or sequence of states exhibited by entities or systems over time or along a conceptual dimension (such as pseudotime). It investigates transitions, changes, and developmental pathways, often aiming to reveal underlying processes, determine fate, or understand dynamic behavior. This approach is significant for providing quantitative and visual insights into complex dynamic processes, such as cellular differentiation or particle motion, by modeling and analyzing data representing these trajectories.