Efficiency, sender utilization, channel utilization(from senders point of view) are same. Its like out of 100% bandwidth alloted to you, how much are you using?
Now, lets say efficiency is 20% and channel bandwidth=400Mbps. So, throughput is how much max bandwidth you can use considering the efficiency of channel.
THus, throughput = efficiency * channel bandwidth
= 20% of 400Mbps
= 80Mbps