What is the meaning of Pigweed?

Any of various weedy plants sometimes used as pig fodder:

  1. Amaranthus species.
  2. Chenopodium album, white goosefoot.

    Amaranthus species.

    Chenopodium album, white goosefoot.

    Portulaca bicolor, of Australia.

    Polygonum aviculare (common knotgrass).

    Heracleum sphondylium.

    Source: wiktionary.org