An Etymological Dictionary of Astronomy and Astrophysics

1. Electronics: The extent to which an → analogue → amplifier boosts the strength of a → signal. Also called
   → gain.
   

2. In → gravitational lensing, the ratio of the lensed brightness to unlensed brightness. This factor depends on the mass of the → lensing object and the
   closeness of the alignment between observer, lens, and source (→ impact parameter).

See also: → amplification; → factor.