The ellipsis (...), also called omission marks or the suspension, has just two uses.
First, the ellipsis is used to show that some material has been omitted from the middle of a direct quotation.
Second, the ellipsis is used to show that a sentence has been left unfinished. Unlike the dash, which is used to show that an utterance has been broken off abruptly (recall the unfortunate General Sedgwick!), the ellipsis shows that the writer or speaker has simply "tailed off" into silence, deliberately leaving something unsaid: