Paraxial is a term that is frequently used in the field of optics, particularly in relation to the behavior of light as it passes through various mediums. It is often used to describe rays of light that are close to the axis of an optical system, and is related to the concept of optical aberrations. Synonyms for the term include "near-axis", "central", "on-axis", "axial", and "collimated". These terms all refer to the same general concept of light rays that are aligned with the optical axis of a system, and are important for understanding how a lens or other optical component will affect the propagation of light.