I'm well aware of the Gardening/Horticultural approach of "a weed is any plant that you don't want in its current location".
But I think most people would agree that there's a more useful interpretation of "weed" that relates to its growth.
I would say that weeds are the plants that would be extremely easy to introduce if you wanted to them in a particular place, and extremely hard to remove if you didn't want them.
Common properties that I can think of, of the top of my head, for such plants include:
- quickly growing.
- quickly reproducing.
- re-growing from roots even if the above-ground plant is removed.
- not particularly sensitive to ground conditions.
Why don't all plants exhibit these behaviours?
It feels relatively "obvious" that the plants that exhibit these behaviours should be able to out-compete plants that don't, since they reproduce faster and are more resilient.
And yet the slightest glance outside demonstrates a wide variety of plants that I think would trivial die if I attempted to attack / damage them.