What is meant by threshold voltage?

Answer: The term “threshold voltage” refers to a specific voltage that, depending on the device, causes a particular phenomenon to occur. 

And it is also defined as the gate – body voltage that causes the surface to change from p – type to n – type. In this situation the surface potential has equal to the negative of the p – type potential.

It determines the measuring the drain current in the linear regime for various gate voltage levels.