The broadest definition of a weed is simply a plant out of place. Now that description may be over reaching, but the implication has merit. The reason being, whatever the plant, it’s depriving water, nutrients and sunlight from the plants you do want there! So even if it’s a plant that doesn’t fit in the classic weed category, if it’s in the wrong place it needs to go. Otherwise, that "weed" is going to compete with your other plants. In this podcast, Joe Lamp'l provides useful strategies for keeping weeds at bay.