Generative engines
Systems that retrieve, synthesise and generate an answer to a query rather than returning a ranked list of documents. The term became central through the 2023 GEO research.
What distinguishes them
A search engine matches and ranks. A generative engine retrieves several documents, reads them and composes a new text that did not exist before. The output is not selected from the corpus, it is written from it.
That single difference produces most of the vocabulary in this A to Z. There is no position to hold, so visibility has to be redefined; there is no click, so measurement has to be redefined; and the answer can be wrong in ways a list cannot.
Retrieval, synthesis, generation
Retrieval decides the candidate set: whether your material is in the running at all. Synthesis decides what gets used. Generation decides how it is phrased and whether you are named.
Most optimisation effort goes into the first stage, which is necessary and not sufficient. Being retrieved and then not used is the ordinary case, not a failure state.