Retardation

Retardation is a general term describing the slowing or delaying of a process, event, or signal relative to a reference. The precise meaning varies by field, but it typically denotes a lag in time, a phase shift, or a reduction in rate. In everyday language, it can refer to delays in mechanical, electronic, or developmental contexts.

In optics, retardation refers to a phase difference between components of a light wave that results from passage through a birefringent material or a wave plate. The amount of retardation is measured as a phase shift in radians or as an optical path difference in nanometers and determines how polarization components emerge after transmission.

In electrical engineering and signal processing, retardation denotes a time delay or phase lag between input and output signals. It is related to group delay, the derivative of the phase response with respect to frequency. Retardation can affect control system stability and is commonly addressed through compensation networks that introduce lead or equalization to minimize adverse effects.

Historically, retardation has been used to describe intellectual disability, a usage now regarded as outdated and offensive in many contexts. Contemporary medical and educational language favors terms such as intellectual disability or developmental delay, depending on the situation. When referencing physical concepts or measurements, retardation remains a neutral scientific term. Related concepts include optical retardation and phase retardation, both describing how delays influence observed phenomena.