Virtual memory is a memory management technique that allows a computer to use hard drive space as if it were additional RAM. This enables systems to run larger applications or multiple applications simultaneously, even if the physical memory is limited. By swapping data between the RAM and the hard drive, virtual memory helps optimize performance and resource utilization. When a program requests more memory than is physically available, the operating system uses a portion of the hard drive, known as the page file or swap space, to temporarily store data. This process is transparent to the user, allowing for a seamless experience while maximizing the efficiency of the system's resources.