Transconductance in mosfets
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.