With Hyper-V, a virtual device is a software module that provides an I/O path for a partition and are configurable via Hyper-V Manager console.  A VDev allows a single physical device attached to the primary partion to be shared across multiple child partitions. Each partition believes it has exclusive access to the device. Virtual devices are very often packaged as a COM device and managed using a WMI interface.
There are two different kinds of Virtual Devices in general:

• Emulated devices also sometimes called Core devices
• Synthetic devices also called Enlightened devices

Synthetic versus Emulated devices

Emulated (legacy) devices emulate a physical network adapter in software. Although this process provides networking services to a virtual machine, it requires
additional host processing resources.

Full Article