The Collaborative International Dictionary of English v.0.48:

baby-walker \baby-walker\ n.
   a framework on small wheels or casters designed to support
   small children while they are learning to walk, and usually
   having a fabric support that permits the child to sit. Called
   also walker and go-cart.

   Syn: walker, go-cart
        [WordNet 1.5 +PJC]

WordNet (r) 3.0 (2006):

baby-walker
    n 1: an enclosing framework on casters or wheels; helps babies
         learn to walk [syn: walker, baby-walker, go-cart]