Definition of "omission"

(uncountable) The act of omitting.  examples

(uncountable) The act of neglecting to perform an action one has an obligation to do.  examples

(countable) An instance of those acts, or the thing left out thereby; something deleted or left out.  examples

Something not done or neglected.  examples

(grammar) The shortening of a word or phrase, using an apostrophe ( ' ) to replace the missing letters, often used to approximate the sound of speech or a specific dialect.  examples