I want to know the answer to the following question:
The terms GMT and Greenwich Mean Time are also used informally to refer to what?
All the background I'm provided with is that "Because the rotational period of Earth is not perfectly constant, the duration of a second would vary if calibrated to a telescope-based standard like GMT or UT—in which a second was defined as a fraction of a day or year.". Is that enough to answer the question?
Answer: no