An ellipsis is most commonly used when a writer is quoting another source but not using the entire quoted sentence, paragraph or page. An ellipsis is put in place of the omitted words or sentences to show that the quote has been condensed.
It is important to ensure that the omission does not change the meaning of the original quote. The aim is to shorten or tighten a long quote by eliminating unnecessary words or sentences, but the overall meaning of the quote should remain intact. In conversational writing, an ellipsis is sometimes used to show a pause or a break in the writer's thought process.