The Collaborative International Dictionary of English v.0.48:

Truck \Truck\, n. [Cf. F. troc.]
   1. Exchange of commodities; barter. --Hakluyt.
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   2. Commodities appropriate for barter, or for small trade;
      small commodities; esp., in the United States, garden
      vegetables raised for the market. [Colloq.]
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   3. The practice of paying wages in goods instead of money; --
      called also truck system.
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   Garden truck, vegetables raised for market. [Colloq.] [U.
      S.]

   Truck farming, raising vegetables for market: market
      gardening. [Colloq. U. S.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

truck farming
    n 1: growing vegetables for the market