Client Hyper-V is a virtualization product that comes installed with Windows 8, but it's not enabled by default.  To enable it follow these steps:

  1. On the Control Panel, click Programs, and then click Programs and Features.
  2. Click Turn Windows features on or off.
  3. Click Hyper-V, click OK, and then click Close.

BTW: There are specific requirements for running Client Hyper-V on Windows 8.  See those here:  Requirements for Running Hyper-V on Windows 8