Ellipsis happens
when we leave out (in other words, when we don’t use) items which we would
normally expect to use in a sentence if we followed the grammatical rules. The
following examples show ellipsis. The items left out are in brackets [ ]:
1. I am absolutely sure [that] I have met her somewhere before.
2. [Have you] Seen my gloves anywhere 3. She
sang and [she] played the violin at the same time.
In fact, when we use ellipsis appropriately, no one thinks we have ‘left out’
anything, and ellipsis is normal and very common, especially in informal
conversation