virtual memory
also: VM, paging, swap memory
A memory management technique that uses disk storage to extend the apparent amount of RAM available to processes, allowing programs to use more memory than physically exists.
Virtual memory abstracts physical RAM by creating a larger logical address space. The operating system maps this logical memory to physical RAM and disk storage (typically in a swap partition or file). When RAM becomes full, the kernel moves inactive memory pages to disk, freeing up physical RAM for active processes.
This enables a system with 8 GB of physical RAM to run programs totaling 16 GB of memory usage. However, disk access is much slower than RAM, so excessive virtual memory use degrades performance noticeably.
For example, a process requesting 12 GB of memory on a 8 GB system can succeed because the kernel will swap unused portions to disk. You can view swap usage with free -h or swapon --show, and configure swap space during system installation or with additional swap files.