A VMDK (Virtual Machine Disk) file is a disk image format used by VMware virtualization products, such as VMware Workstation, VMware ESXi, and VMware vSphere. It essentially represents a virtual hard drive. A single VMDK file, or a set of VMDK files, contains the complete contents of a virtual machine's hard drive, including the operating system, applications, user data, and configuration settings. These files can be used to create, store, and manage virtual machines. VMDK files allow for portability and easy backup of virtual machines. They can be copied, moved, and restored, making them ideal for disaster recovery and testing purposes. The format supports various disk types, including pre-allocated, thin-provisioned, and sparse disks, offering flexibility in storage management. VMDK files are crucial for virtualization environments, enabling the creation and management of multiple virtual machines on a single physical host.