Parallels Compressor is installed only into your Windows virtual machines along with Parallels Tools. Parallels Tools are a set of special utilities designed to help you use your virtual machines in the most comfortable and efficient way.
For the list of Windows guest OSs which support Parallels Tools and Parallels Compressor, see the main product's Help.
Note: Parallels Compressor is not available for virtual machines that use physical partitions as their hard disks (for example, Boot Camp virtual machines on Mac host computers).