A pathline (Figures 1) is the continuous (usually smooth) trajectory of a single particle under investigation over time that shows the particle's temporal-spatial behavior governed by the underlying flow. A timeline (Figure 2) is a time-varying curve (not necessarily smooth) that connects a set of particles simultaneously released along an initial line (i.e., rake line, usually perpendicular to the local flow direction). Analogous to a rope released in and then warped by the flow, a timeline reveals the change in the direction orthogonal to the flow and hence is well suited for showing flow convergence and divergence. A streakline (Figure 3) is also a time-varying curve (the smoothness depends on the particle release interval) that connects a sequence of particles successively released from a fixed position to depict the change of the flow direction over time. A streakline emulates how a block of dye, released at a specified position in the flow, propagates to make a visual pattern. Animated streaklines (5.49M) are often used for unsteady flow visualization. Pathlines and streaklines are identical to streamlines in a steady flow, but different from one another in an unsteady flow (Figure 4).