Population inversion is a physical condition where more atoms or molecules in a system occupy a higher energy state than a lower energy (ground) state. This unusual distribution is essential for the operation of lasers and masers, as it enables stimulated emission of radiation. In cybersecurity, the term is rarely used directly, but understanding population inversion is important in the context of quantum cryptography and secure communications, where lasers play a key role. Achieving and maintaining population inversion typically requires external energy input, known as pumping.