the omission from speech or writing of a word or words that are superfluous or able to be understood from contextual clues

it is very rare for an ellipsis to occur without a linguistic antecedent

an example of ellipsis

a regular oval shape, traced by a point moving in a plane so that the sum of its distances from two other points (the foci) is constant, or resulting when a cone is cut by an oblique plane which does not intersect the base