Information gain
Information gain refers to what a page contributes that pages already ranking do not: original data, field measurements, an angle absent from existing results. Search engines reward this surplus rather than rewording the existing consensus.
In practice
The concept, drawn from a Google patent, shapes every page our engine produces: each page must contain five to seven elements no direct competitor displays — actual distances between towns, demographic data, verifiable local specifics. Rewriting what ten pages already say has never produced lasting ranking improvement.