The Collaborative International Dictionary of English v.0.48:

groundcover \ground"cov`er\, ground cover \ground" cov`er\n.
   1. low-growing plants planted in deep shade or on a steep
      slope where turf is difficult to grow.
      [WordNet 1.5]

   2. small plants other than saplings growing on a forest
      floor.

   Syn: ground cover, undergrowth.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

ground cover
    n 1: low-growing plants planted in deep shade or on a steep
         slope where turf is difficult to grow [syn: groundcover,
         ground cover]
    2: small plants other than saplings growing on a forest floor
       [syn: groundcover, ground cover]