ISO Invariance
The property of a sensor whose noise is essentially the same whether a file is brightened by raising ISO in camera or by lifting exposure in processing.
In depth
An ISO-invariant sensor has read noise low enough that downstream electronics contribute almost nothing, so the amplification stage no longer matters. This lets a photographer shoot at base ISO to protect highlights and lift the shadows afterwards. Few cameras are perfectly invariant, and most have a threshold above which they become so.
Examples in practice
On an invariant sensor, an ISO 100 file lifted four stops matches an ISO 1600 file almost exactly for noise.