Source : Webster's Revised Unabridged Dictionary (1913)

Inboard \In"board`\, a. & adv.
   1. (Naut.) Inside the line of a vessel's bulwarks or hull;
      the opposite of outboard; as, an inboard cargo; haul the
      boom inboard.

   2. (Mech.) From without inward; toward the inside; as, the
      inboard stroke of a steam engine piston, the inward or
      return stroke.

Source : WordNet®

inboard
     adj : located within the hull or nearest the midline of a vessel
           or aircraft; "the inboard flaps on the wing" [ant: {outboard}]