Virtual memory is a computer system technique that allows a computer to use more memory than is physically available. It does this by temporarily transferring data from the RAM (Random Access Memory) to a reserved space on the hard drive, known as the page file or swap space. This process enables the system to run larger applications and manage multiple tasks simultaneously without running out of memory. When a program needs more memory than what is available in RAM, the operating system moves some data to the hard drive, freeing up space in RAM for the new data. This allows for efficient multitasking and helps prevent crashes, although accessing data from the hard drive is slower than accessing it from RAM.