An ellipsis, composed of three spaced periods or the ellipsis character, signifies either omission or trailing thought. Write an ellipsis using three periods with non-breaking internal spaces (option-shift-space on Mac, ctrl-shift-space on Windows) and regular spaces on either side: I am . . . a spaced ellipsis. While this is the preferred method of Bryan A. Garner, The Chicago Manual of Style, APA style, and my writing, The Elements of Typographic Style suggests using the ellipsis unicode character: I am … an ellipsis character. No matter your choice, stick with it—editors will have a far easier time changing a uniform habit than a non-uniform habit for their publishing conventions.
In technical writing, reserve ellipses for omitting words, phrases, or sentences from quoted material, though be careful not to change the quoted material’s original intention. Thus, The film, which covered romances and car chases, was a waste of time can become The film . . . was a waste of time. Avoid beginning with an ellipsis, even when quoting from within a sentence. When ending with an ellipsis, if the last word ends the source sentence, write a period followed by an ellipsis, otherwise write an ellipsis followed by a period: The book was good. . . . or, if more follows the last word, The book was good . . . . These four-period situations may convince you to prefer the spaced ellipsis over the ellipsis character, as the ellipsis charcater, when beside a period, looks like an unbalanced mistype: The book was good. . . . vs. The book was good. …
In creative writing, ellipses can also symbolize trailing thought: I drove down the road . . . so and my car needs an oil change. Do not use ellipses to symbolize interruptions; that task belongs to the em dash (see hyphens and dashes).