A spin exchange relaxation-free (SERF) magnetometer is a type of magnetometer developed at Princeton University in the early 2000s. SERF magnetometers measure magnetic fields by using lasers to detect the interaction between alkali metal atoms in a vapor and the magnetic field.

Serfdom is the status of many peasants under feudalism, specifically relating to manorialism. It was a condition of bondage, which developed primarily during the High Middle Ages in Europe and lasted in some countries until the mid-19th century.