Virtual memory is a feature of an operating system that enables a computer to be able to compensate shortages of physical memory by transferring pages of data from random access memory to disk storage.
This process is done temporarily and is designed to work as a combination of RAM and space on the hard disk.
This means that when RAM runs low, virtual memory can move data from it to a space called a paging file. This process allows for RAM to be freed up so that a computer can complete the task.
Occasionally a user might be shown a message that says the virtual memory is running low, this means that either more RAM needs to be added, or the size of the paging file needs to be increased.