What exactly does it mean when we say 'increase the transconductance of a mosfet'? What is the advantage of having a high transconductance mosfet?
A MOSFET is a transconductance device in that an input voltage controls an output current or, in terms of gain, current out / voltage in. Current/voltage is conductance and the word "trans" is placed in front of the word "conductance" to imply the main operating parameter of such a device.
So a device with more transconductance means that it produces a bigger change in output current for a change in input voltage. Not always desirable of course but pretty useful in a lot of applications.