Looks like Forget me nots, but hard to tell at this stage. You might have to wait until they bloom!

Not forget me nots - looks like a clump of some herbaceous perennial,the way its growing, not a weed as such, although a weed is only a plant you don't want really. Looks a bit like Shasta daisy foliage (Leucanthemum superbum) but that should have flowered and finished by now, so unless you cut it right down and its growing again, its probably not that. Maybe some other late flowering perennial, such as one of the Helianthus varieties or Helenium or Rudbeckia, wait and see what it produces.

And whether its a weed or not its still a plant...

reminds me of Physostegia the obedient plant. but mine is a bout 2 ft tall now.

Looks a bit like some Campanulas too.