Thanks for the help!
But, I already read that page and it seems that it doesn't define the meaning of cross conduction. It only tells how to prevent this cross conduction.
May I have a deeper understanding of it.
I had the same question. See Question 45 in this book: https://goo.gl/RGIpr. That discusses switching power supplies, but I think "cross-conduction" is more general. You have a situation where there are two transistors, only one of which should be on at any given time. For example, you might be selecting one of two power inputs (IN1 and IN2) to be connected to a single output (OUT) in a power mux. Each input is connected to the drain of a different NMOS, and both NMOS's source gates are connected to the single output OUT. At any given time, only one of the NMOS's should be on. If they were both on at the same time (perhaps briefly during the switchover), you'd have a conducting path between IN1 and IN2. This would be an example of cross-conduction. I'm not an expert, though, so take that with a grain of salt.