Virtual machine VM
Simulated computer running on a physical host via a hypervisor. Own OS, own resources, isolated from host and other VMs.
Two main types: system VM (whole computer, e.g. VirtualBox, EC2 instance) and process VM (runs a program, e.g. JVM, .NET CLR). System VMs are the foundation of the cloud (AWS EC2, GCP Compute Engine = VMs under the hood). Containers are the lightweight alternative — share the kernel, more efficient but less isolation. Microvm (Firecracker, AWS Lambda) is a hybrid between VM and container.