These are all names for the omission of one word or several in statements of comparison: Grades for this semester were much lower than last semester. Those for before last semester was omitted, and the ellipsis thus slightly mars the parallelism. Omitting such small words is common in Casual and Impromptu speech, and ordinarily no one becomes confused, but in all but the most Informal writing, clarity and reader comfort will be improved if you omit no words whose absence mars the parallelism. See AS GOOD OR BETTER THAN; ELLIPSIS (1).
