Source : Webster's Revised Unabridged Dictionary (1913)

Terra incognita \Ter"ra in*cog"ni*ta\ [L.]
   An unknown land; unexplored country.

         The enormous tracts lying outside China proper, still
         almost terr[ae] incognit[ae].            --A. R.
                                                  Colquhoun.

Source : WordNet®

terra incognita
     n : an unknown and unexplored region; "they came like angels out
         the unknown" [syn: {unknown}, {unknown region}]