The Collaborative International Dictionary of English v.0.48:

Gibberish \Gib"ber*ish\, a.
   Unmeaning; as, gibberish language.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

gibberish \gib"ber*ish\ (j[i^]b"b[~e]r*[i^]sh or
   g[i^]b"b[~e]r*[i^]sh), n. [From Gibber, v. i.]
   1. Rapid and inarticulate talk; unintelligible language;
      unmeaning words.
      [1913 Webster]

            He, like a gypsy, oftentimes would go;
            All kinds of gibberish he had learnt to know.
                                                  --Drayton.
      [1913 Webster]

            Such gibberish as children may be heard amusing
            themselves with.                      --Hawthorne.
      [1913 Webster]

   2. Incomprehensible, obscure, or pretentious technical talk
      or writing; excessively obscure jargon.
      [PJC]

WordNet (r) 3.0 (2006):

gibberish
    n 1: unintelligible talking [syn: gibberish, gibber]