@replacement

When a grammar rule replaces A with B, the A is said to be the original (/sthAnin) and the B is said to be the replacement (/Adeza).

AFI, when rule atobhisa::ais replaces deva- देवॱ + /bhis with deva- देवॱ + ais ऐस्,

the /bhis is the sthAnI स्थानी (original),
and the ais ऐस् is the AdezaH आदेशः (replacement).

Some sUtras that use the word /sthAnin —

Some sUtras that use sthAna- स्थानॱ "place" or sthAne स्थाने "in the place of" —

Some sUtras that use the word /Adeza —

The word /Adeza has another meaning of "teaching", as used in Adezapraty....