Nothing

Nothing represents an element of a list that will automatically be removed.

Examples

Nothing disappears from lists:

{1, 2, Nothing, 3, Nothing, 4}
(* {1, 2, 3, 4} *)

Conditionally remove elements:

Table[If[OddQ[n], n, Nothing], {n, 1, 6}]
(* {1, 3, 5} *)

Please visit the official Wolfram Language Reference for more details.