A virtual machine is a software-based emulation of a physical computer that allows multiple operating systems to run on a single physical machine. Each virtual machine runs its own operating system and applications in an isolated environment, as if it were a physical machine. This makes it possible to run multiple operating systems and applications on a single physical machine, without having to buy and maintain multiple physical machines. Virtual machines are widely used in cloud computing, data centers, and other environments where efficient resource utilization and isolation are important.