The boundary layer on a flat plate is called laminar boundary layer if

Explanation:

Reynold's number: 

• It is a dimensionless number that determines the nature of the flow of liquid through a pipe or flat plate. 
• It is defined as the ratio of the inertial force to the viscous force for a flowing fluid.
• Reynold's number is written as Re.
• \({Re} = \frac{{{\rm{Inertial\;force}}}}{{{\rm{Viscous\;force}}}}\)

Flat plate flow:

• If Reynold's number lies below 5 × 105, then the flow of liquid is streamlined or laminar.
• If Reynold's number is greater than or equal to 5 × 105, the flow of liquid is turbulent.

Additional Information

Pipe flow : 

• If Reynold's number lies between 0 - 2000, then the flow of liquid is streamlined or laminar.
• If Reynold's number lies between 2000 - 3000, the flow of liquid is unstable and changing from streamline to turbulent flow. 
• If Reynold's number is above 3000, the flow of liquid is turbulent.