Unhelpful: “A weed is just a plant in the wrong place”
You can eat almost anything, apart from the few things that millennia of trial-and-error have proved you shouldn’t, and even then there are ways (e.g. blanched nettle leaves lose the sting).
I discovered last year that goosegrass (for which everyone seems to invent the name stickyweed) is quite pleasant when young & fresh. I’m hoping to eat it into extinction.