Ellipsis

Ellipsis is the deliberate omission of a word or phrase that the reader can recover from the surrounding sentence, so the construction is understood without being repeated.

She took the first train; her brother, the last.

The second clause has no verb. Took is understood from the first, and the reader supplies it without noticing they have done any work. That is ellipsis as a figure of speech, and it is not the same thing as the three dots, which are a punctuation mark that happens to share the name.

The effect is speed and a certain dryness. The omission implies that the sentence has better things to do than repeat itself, and it makes the reader an active participant in the line.

• Full: Some editors cut what is weak. Other editors cut what is merely unnecessary.
• Elliptical: Some editors cut what is weak; others, what is merely unnecessary.

It is everywhere in dialogue, because speech is elliptical by nature. Coming? Not tonight. Neither is a grammatical sentence and both are perfectly clear, which is why heavily elliptical dialogue reads as natural and fully grammatical dialogue reads as stilted. It also does quiet work in oblique dialogue, where what a character leaves out is the point.

One limit: the omitted element must be recoverable exactly. If the reader has to supply a slightly different word, the sentence reads as an error rather than a compression.