A weed is a plant considered undesirable in a particular situation, “a plant in the wrong place”. Examples commonly are plants unwanted in human-controlled settings, such as farm fields, gardens, lawns, and parks. Taxonomically, the term “weed” has no botanical significance, because a plant that is a weed in one context is not a weed when growing in a situation where it is in fact wanted, and where one species of plant is a valuable crop plant, another species in the same genus might be a serious weed, such as a wild bramble growing among cultivated loganberries. In the same way, volunteer crops (plants) are regarded as weeds in a subsequent crop. Many plants that people widely regard as weeds also are intentionally grown in gardens and other cultivated settings, in which case they are sometimes called beneficial weeds. The term weed also is applied to any plant that grows or reproduces aggressively, or is invasive outside its native habitat. More broadly, “weed” occasionally is applied pejoratively to species outside the plant kingdom, species that can survive in diverse environments and reproduce quickly; in this sense it has even been applied to humans.
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BillyScraps 
Yes, it’s all a matter of definition. When we ran the project on the farm I used to grow nettles and fat hen as part of the foraging courses – got there one day to set up, went behind the polytunnel to cut nettles and found the farmer had killed them all. No nettle soup and the farmer (who wanted me to run the foraging courses) just kept repeating “They’re weeds.”
Idiot. It still annoys me, as you may have guessed.
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That is frustratingly knuckle-headed.
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He had tunnel vision and a deficiency in brain power. It’s what happens when cousins marry and leave farms to the next generation.
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