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A pathline is a fluid particle's material trajectory through a time-dependent velocity field. Unlike a streamline, which follows the velocity field at one frozen time, a pathline solves the displayed ODE. The two curves coincide in a steady flow but generally differ in an unsteady one.

The region bounded by the dividing streamlines of a two-dimensional point source superposed on uniform flow. Its stagnation point is $-Q/(2\pi U)$ upstream and its far downstream width is $Q/U$. The boundary encloses fluid originating at the source rather than a rigid obstacle; the upstream stagnation point is reached only asymptotically by the upstream source trajectory.

In steady flow, the velocity and other relevant flow fields are independent of time in the chosen reference frame. Streamlines then coincide with the paths of moving particles, while convective acceleration can still be nonzero.

For steady flow of constant-density fluid in a uniformly rotating frame with conservative body forces, the displayed quantity is constant along each relative streamline. The centrifugal potential contributes the negative quadratic term, and the Coriolis force contributes no work because it is perpendicular to the relative velocity. The result follows by dotting the rotating Euler equations for an inviscid fluid with that velocity.

A stream tube is a narrow tube whose side boundary consists of streamlines. In steady flow no fluid crosses its sides, so continuity makes its mass flux $A\rho u$ constant. If flow follows a magnetic field with constant magnetohydrodynamic mass loading, its normal area obeys $A|\mathbf{B}|=\mathrm{constant}$.