Computing term for a software-based emulation of a physical computer.
I use a virtual machine as my development environment.
仮想計算機上で別のOSを動かすことができる。
You can run another OS on a virtual machine.
エミュレータ is a broader term for hardware or software that mimics another system, while 仮想計算機 specifically refers to a virtualized computer environment.
Compound of 仮想 (virtual) and 計算機 (computer).