A weed is a plant considered undesirable in a particular situation, growing where it conflicts with human preferences, needs, or goals. Plants with characteristics that make them hazardous, aesthetica
Weeds growing in the cracks of a concrete staircase (Epilobium roseum, Chelidonium majus, Oxalis corniculata, Plantago major)
A dandelion is a common plant all over the world, especially in Europe, Asia, and the Americas. It is considered a weed in some contexts (such as lawns) but not others (such as when it is grown as a vegetable or herbal medicine).