Hello guys, I don't understand the meaning of this line

"The FET has a high incremental drain impedance, giving roughly constant current for VDS greater than a volt or two"

from field-effect transistors chapter of the book "The art of electronics".
Here what does it means by "high incremental drain impedance" Can anyone help me to understand it?

 

"high incremental drain impedance" means the change in drain current for a change in drain voltage is very low, thus ΔV /ΔI = R is very high, making the drain look like a near constant-current device.