Source : Webster's Revised Unabridged Dictionary (1913)

Roger \Rog"er\, n. [From a proper name Roger.]
   A black flag with white skull and crossbones, formerly used
   by pirates; -- called also {Jolly Roger}.

Source : WordNet®

Jolly Roger
     n : a black flag bearing a white skull and crossbones; indicates
         a pirate ship [syn: {black flag}, {pirate flag}]