What is meant by a 'virtual machine' in computing?

A 'virtual machine' in computing refers to an emulated environment that allows software to run as if it were on its own physical machine. This concept enables multiple operating systems to coexist on a single physical machine, providing flexibility and efficiency in resource utilization. A virtual machine effectively simulates an entire hardware environment, allowing software to run without needing to modify it for the underlying hardware, which is particularly useful for testing, development, and running applications that may not be compatible with the host system's operating system.

The correct answer captures this essence by highlighting the virtualization of a specific computer system. This means the virtual machine mimics the architecture and functionality of a real machine, allowing applications designed for that architecture to run seamlessly.

Other options refer to different aspects of computing; for instance, an application that compiles source code focuses on converting code to executable form, which is not the function of a virtual machine. A programming language is a set of instructions for computers, not an environment for execution. An execution environment that runs programs, while somewhat aligned with the concept, does not convey the full scope of virtualization and emulation that defines a virtual machine.