Definition of weed: a plant that grows spontaneously in a crop and whose presence is more or less harmful to the crop. (Weeds are harmful because they compete with cultivated plants for water, light and mineral elements in the soil). – Larousse
These are the plants that many people call weeds, the unloved ones. It’s worth noting that all plants try to thrive but weeds are the ones that have had the most success in adapting, often aided by the war waged against them by man. It’s also worth noting that many of these weeds are powerful medicinal plants. Seeing their usefulness doesn’t make them any less invasive, but it does reduce losses.
Dandelions are a good example of a weed.