The Collaborative International Dictionary of English v.0.48:

Herbage \Herb"age\ (?; 48), n. [F. See Herb.]
   [1913 Webster]
   1. Herbs collectively; green food beasts; grass; pasture.
      "Thin herbage in the plaims." --Dryden.
      [1913 Webster]

   2. (Law.) The liberty or right of pasture in the forest or in
      the grounds of another man. --Blount.
      [1913 Webster]

WordNet (r) 3.0 (2006):

herbage
    n 1: succulent herbaceous vegetation of pasture land [syn:
         herbage, pasturage]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

HERBAGE, English Law, A species of easement, which consists in the right to
feed one's cattle on another man's ground.