1. [n]  a quantity of no importance; "it looked like nothing I had ever seen before"; "reduced to nil all the work we had done"; "we racked up a pathetic goose egg"; "it was all for naught"; "I didn't hear zilch about it"
2. [adj]  (law) lacking any legal or binding force; "null and void"

1. \Null\, a. [L. nullus not any, none; ne not + ullus any, a
   dim. of unus one; cf. F. nul. See {No}, and {One}, and cf.
   {None}.]
   Of no legal or binding force or validity; of no efficacy;
   invalid; void; nugatory; useless.
   
         Faultily faultless, icily regular, splendidly null,
         Dead perfection; no more.                --Tennyson.
   
   

2. \Null\, n.
   1. Something that has no force or meaning.
   
   2. That which has no value; a cipher; zero. --Bacon.
   
   {Null method} (Physics.), a zero method. See under {Zero}.
   
   

3. \Null\, v. t. [From null, a., or perh. abbrev. from annul.]
   To annul. [Obs.] --Milton.
   
   

4. \Null\, n. [Etymol. uncertain.]
   One of the beads in nulled work.
   
   

A special value used in several languages to represent the thing referred to by an uninitialised pointer.

A special value that may be stored in some database columns to represent an unknown, missing, not applicable, or undefined value. Nulls are treated completely differently from ordinary values when evaluating SQL expressions and there are several SQL constructs for dealing with nulls.