Virtualization comes with a lot of jargon. This virtualization glossary explains the terms you will meet when renting a VPS or running your own hypervisor, with links to deeper guides.
Before you start
- For the big picture, read what virtualization is.
Core terms
- Hypervisor: software that creates and runs virtual machines. See type 1 vs type 2.
- Host: the physical server running the hypervisor.
- Guest / VM: a virtual machine with its own OS.
- VPS: a virtual private server rented from a provider; see how a VPS works.
- KVM: the Linux kernel's built-in hypervisor.
- QEMU: the emulator/device model KVM uses to present virtual hardware.
- libvirt / virsh: the management API and command-line tool for KVM; see virsh cheat sheet.
CPU and memory
- vCPU: a virtual CPU, scheduled on physical cores or threads.
- Overcommit: selling more vCPUs or RAM than physically exist, relying on not all VMs being busy.
- Steal time: time a vCPU waited for the physical CPU; see steal time explained.
- CPU pinning: tying vCPUs to specific physical cores.
- Ballooning: reclaiming unused guest memory; KSM merges identical memory pages.
- VT-x / AMD-V: CPU extensions for hardware-assisted virtualization.
- Nested virtualization: running a hypervisor inside a VM.
Storage
- qcow2 / raw: VM disk image formats; see qcow2 vs raw.
- Thin provisioning: disk space allocated only when written.
- LVM, ZFS, Ceph: storage layers for VM disks.
- Snapshot: point-in-time state of a VM disk; not a backup. See snapshot vs backup.
- IOPS: input/output operations per second, a disk performance measure.
Devices and networking
- VirtIO: paravirtualized drivers for fast disk and network.
- Bridge: a virtual switch connecting VMs to the network.
- NAT: private VM addresses sharing the host's public IP.
- VLAN: a tagged, isolated network segment.
- PCI passthrough: giving a VM direct access to a physical device.
Operations
- Live migration: moving a running VM to another host.
- Template / golden image: a prepared VM image for fast cloning.
- cloud-init: configures a VM at first boot.
- Guest agent: a helper inside the VM for clean shutdowns and consistent backups.
- VNC console: remote screen access to a VM from the panel.
- Rescue mode: booting a recovery system to repair a VM.
Containers
- Container: isolated processes sharing the host kernel; see containers vs VMs.
- LXC / OpenVZ: system container technologies used for container-based VPSs.
- Docker / Podman: application container tools.
- MicroVM: a minimal, fast-booting VM for sandboxes.
Frequently asked questions
Is a vCPU the same as a CPU core?
Not necessarily; it may be a time share of a core or a hardware thread.
What is the difference between a VPS and a VM?
A VPS is a VM sold as a hosting product with network, IPs and a panel.
Where can I find general hosting terms?
See the web hosting glossary.