Transformational generative grammar is a set of grammar rules that are used when basic clauses are combined to form more complex sentences.
An example of transformational generative is the idea that sentences have surface structure and deep structure levels.
transformational (generative) grammar
Linguis. a system of linguistic analysis consisting of a set of rules that generate basic syntactic structures, in the form of simple independent clauses, and a set of transformational rules that operate on those structures so as to produce questions, complex sentences, etc. and thus to account for every possible sentence of a language