Virtual Box
https://www.virtualbox.org/ is one of the programs that make VM (Virtual Machine) that is essentially an emulator that can run other OS within host OS in this case Windows. Another one is VMware
VMware Virtualization for Desktop & Server, Application, Public & Hybrid Clouds | United States . Basically it shares part of disk, few cores of the processor and part of RAM with host system and is pretty well isolated from host OS. You can install guest OS or even run live like Linux. Drawback is that it has access to HW just as much as host OS would let it.
Dual BOOT is when you install another OS next to first one on another partition on disk or even better on another disk. In either case on first boot disk/partition both (or more) OSs can make a menu which upon booting to it you can choose which OS you will use. You can also allow or restrict access to other disk partition.