Explain streamlines and streamline flow.

(N/A) The path of motion of a fluid particle is called a line of flow.
$A$ streamline is defined as a curve whose tangent at any point is in the direction of the fluid velocity at that point.
In a steady flow,the path taken by a fluid particle is a streamline. Figure $(a)$ shows a typical trajectory of a fluid particle,which represents a streamline. The velocity of the particle at any point is in the direction of the tangent drawn at that point.
Streamline flow is defined as a flow in which streamlines can be clearly defined. This occurs when the velocity of the fluid at any given point remains constant over time.
In unsteady flow,the velocity at a point changes with time,so while the path of a particle (line of flow) can be defined,a fixed streamline cannot be defined.