What is " Q oss" FET parameter?

[fonograph]

I am looking at FET transistor datasheet and there is list of capacitances,total gate,gate > source,gate > drain but then there is this Qoss charge with quite high capacitance,what is it? What should I think about it? When does engineer need the Qoss value? In what scenario does it become important?

I am looking at two different transistors,they are very similiar,this is their capacitances

                transistor 1           transistor 2

QG                       3.4                  6.2

QGS                     1.1                  2.4

QGD                   0.55                  0.9

QOSS                   16                   11.5


For switch mode power supply,whitch one would you choose? Their breakdown voltage and on resistance is same.The Qoss was measured at same voltage for both of them,50V.The transistor 1 have lower capacitance across the board except much higher Qoss,I dont know what to think about it,I would like to know what that Qoss is so I can judge it and pick best transistor.

[fonograph]

loss? Isnt Qoss capacitance? Its measured in nano coulomb,so I thought it works like parasitic capacitance when hard switching.Does that mean that if the transistor is switched faster with more powerfull gate driver,then Qoss will be lower becose the transistor spends less time in the intermediate region between on and off?

Is it like energy that will be dissipated becose of the resistance when the transistor is changing from ON to OFF? Is that it?

[fonograph]

ooooOOOOO I understand it! Thank you very much for explanation.   

EDIT : Can you tell me more about that Qoss? Where is it created? I expect it exist between source and drain,is that correct?