The Collaborative International Dictionary of English v.0.48:

Midgard \Mid"gard\ (m[i^]d"g[aum]rd), n. Also Midgarth
\Mid"garth\ (-g[aum]r[th]), Mithgarthr \Mith"garthr\ (Icel.
   m[-e][th]"g[aum]r[th]r'). [Icel. mi[eth]gar[eth]r.] (Teut.
   Myth.)
   The middle space or region between heaven and hell, the abode
   of human beings; the earth.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

Midgard
    n 1: (Norse mythology) the abode of humans in Norse mythology