Emulator does emulate a real hardware. This could be board or CPU or any hardware device. There is a cost associated with the performance when an emulator is used as emulator runs on a user space as a program. Qemu is one of the most used emulator to emulate a board or CPU.
Virtualization virtualise the real hardware. The real hardware is virtually shared by the guest operating system. Multiple types of virtualization possible. VMWare ESX is one of the popular virtualization software. With Intel hardware support the virtualization software can perform very similar to a single system and can make use of the system resources to its maximum.