'single-phase' originates from the combination of 'single,' meaning 'one,' and 'phase,' referring to a stage in a process or cycle, particularly in electrical contexts.

The term 'single-phase' evolved from the need to describe electrical systems that use one phase of alternating current, as opposed to 'three-phase' systems.

Initially, it referred to any singular stage or phase, but it has become more specialized in electrical engineering to denote systems using one AC phase.