This page is about a technical term used in describing language. There is a separate page on the use of ellipsis in punctuation.
(This page forms part of a Course in Figures of Speech. You can find an introduction to it at Figures of Speech course. This page can stand on its own, as well. You may have accessed it from a page on a particular example.)
There are two common figures of speech to do with making writing shorter by leaving things out - figures of contraction. Where elision is about the omission of letters, ellipsis is about the omission of words. This is common in ordinary speech. We ask "Going out tonight?", where "Are you going out tonight?" would strike us as too formal, or indeed pompous. Shakespeare has Macbethâ€™s two sons say, as they prepare to escape to avoid a charge of murder, "I'll to England."/"To Ireland, I" instead of "Iâ€™ll go to England"/"Iâ€™ll go to Ireland." In this case, the ellipsis helps to convey their sense of speed and urgency. (It is also appropriate to the metre.)