subjacency
Subjacency is a concept in formal linguistics, particularly within generative grammar, that describes a condition on the movement of syntactic constituents. Proposed by Noam Chomsky in the 1970s, the subjacency condition aims to explain why certain types of grammatical transformations are permissible while others are not. It is a constraint that restricts how far a constituent can move across certain types of phrasal boundaries.
The core idea of subjacency is that a constituent cannot move out of more than one "subjacency
For example, in English, a wh-phrase (like "what") can move from its original position to the front