Live migration compression, also called live migration with compression, is a default setting in Windows Server 2012 R2 that compresses a virtual machine's (VM's) memory prior to transmitting it to a target host.
Compression reduces bandwidth consumption and can decrease the amount of time required to migrate a live VM by half. Once the VM reaches its destination, its memory is decompressed. Microsoft includes performance counters with Live Migration compression that allow administrators to see what see exactly which CPU resources are being used for compression and how much data is being compressed.
See also: live migration