What is a Weed?

My mom has always said, "A weed is just a plant that no one has found a use for yet." It seems reasonable enough for me. But, who decides what is useful and what is not? Who says this plant below is not as pretty or as useful as a lily or a viola? When it comes to pulling weeds, I know that I must do it to allow my vegetable garden to reach its full potential, but I hate to do it. It just seems wrong to take away all those little plants and maple tree seedlings that pop up in my garden almost on a daily basis. Maybe I should designate a small part of the garden to weeds. Don't they deserve a chance at life too?

I pulled this out this morning. It is now sitting in a teacup next to my computer screen.