In Wiki: A model transformation in Model Driven Engineering takes as input a model conforming to a given metamodel and produces as output another model conforming to a given metamodel.

In Wiki: Model Transformation Language in systems and software engineering is a language for model transformation

In Wiki: A transformation language is a computer language designed to transform some input text in a certain formal language into a modified output text that meets some specific goal.

Some links:

  1. A Taxonomy of Model Transformations (see).