Streamline
A streamline is a concept used in fluid dynamics to describe the path followed by a particle in a fluid flow. It is an imaginary line that is drawn in such a way that the tangent to the line at any point gives the direction of the velocity of the fluid at that point. In other words, a streamline is a line that is everywhere tangent to the velocity vector at each point along its length.

Characteristics of a Streamline
A streamline possesses the following characteristics:

1. Tangent to Velocity Vector: A streamline is a line on which the tangent drawn at any point gives the direction of the velocity of the fluid at that point. This means that the velocity vector is always parallel to the streamline.

2. No Flow Across a Streamline: Along a streamline, there is no flow across the line. This means that the fluid particles move along the streamline without crossing it. The streamline acts as a boundary between regions with different flow characteristics.

3. Continuous and Smooth: Streamlines are continuous and smooth curves that can be traced throughout the flow field. They do not intersect or cross each other.

4. Different Streamlines: In a fluid flow, multiple streamlines can exist, representing different paths followed by different fluid particles. Each streamline represents the path followed by a specific fluid particle.

Significance of Streamlines
Streamlines are an important tool in fluid dynamics for visualizing and analyzing fluid flows. They provide a clear representation of the flow patterns, direction, and velocity of the fluid at different points in the flow field. By following the streamlines, one can understand how fluid particles move and how the flow changes in different regions.

Streamlines also help in determining important flow properties such as the presence of stagnation points, separation points, and vortex formation. They are used in various engineering applications, such as in the design of aerodynamic shapes, flow visualization, and analysis of fluid behavior.

Conclusion
In conclusion, a streamline is a line that is everywhere tangent to the velocity vector at each point. It represents the path followed by a fluid particle in a flow field and provides valuable information about the flow characteristics. By following the streamlines, one can understand the direction, velocity, and behavior of the fluid at different points in the flow.