What is a weed?

We know weeds as plants that grow where they are not wanted. Though dandelions are cultivated for fresh greens, they are out of place in a neatly manicured lawn and hence they are weeds. People living in the cities love wildflowers like daisies and buttercups. But a farmer does not like to see them in his hay field. Weeds are able to grow rapidly and vigorously and this is why gardeners abhor them. Weeds are better survivors than cultivated plants.