Skeleton

Skeleton[n] represents a sequence of n omitted elements in an expression printed with Short or Shallow.

Examples

Skeleton appears in shortened output:

Short[Range[100]]
(* {1, 2, <<96>>, 99, 100} *)

The <<96>> is a Skeleton:

InputForm[Short[Range[10]]]
(* {1, 2, Skeleton[6], 9, 10} *)

Please visit the official Wolfram Language Reference for more details.