Is there any biological distinction between herbs and weeds? I always think of a weed as merely a plant you don't want in a particular place, and/or one you don't (yet) know how to use. But perhaps there is a real difference?
After I cleared all the plantain weed out of my lawn and flower beds, I learned that they actually have uses similar to comfrey. So now I have it planted in my herb bed; though it is a pity it's not got more attractive flowers. Dandelions, which are so bright and cheerful, are good tonic for the liver, and the flowers can be battered and fried into donut holes with the kids
I use lavender, calendula, comfrey, and plantain in healing salves and hand cream. I'm looking for uses for sage, chives, lemon balm, dill, nasturtium and false strawberry. And real strawberry!
Yeah, I feel the same way,up to a point.
Pokeweed and bindweed are are not worth the troubles they bring with them.
Ground Ivy is welcome,on the otherhand,along with many others.
The thing I spend most time killing? Grass.
Hate the stuff.
The original question is pretty easy for me to answer, Weed = a plant that humans have decided they don't want in the place it is currently growing.
Commonly the plants humans have assigned the name weed to are primary succession plants whose roll in nature is to grow roots into dirt so that it can start becoming soil.
Some of the "nitrogen fixers" are lumped into the weed category because they tend to grow in areas of low soil nitrogen content, they are part of the lower end of succession.
As for Biological distinctions, there are none, herb is also a human classification, based on the uses humans have found for various succession plants.
All the comments above are right on, and then additionally, I have found that some herbs that I plant become weeds! There is mint, infamous for getting much larger and aggressive than expected, and there are annuals that may be hard to start intentionally the first time but then self seed vigorously. In my experience this happens with dill, anise hyssop, Dracocephalum moldavica (a nice lemony herb used where I live), lots of flowers like marigolds and bachelors buttons, and if I let them go to seed, then arugula and mustard.
Works at a residential alternative high school in the Himalayas SECMOL.org . "Back home" is Cape Cod, E Coast USA.