Looks like a mixture of wild grass and, possibly, barley. Very likely from a bird feeder, pull it up and put in the brown bin, not your compost.

Thanks very much.

Looks more like wheat than barley to me but as MG says, pull it up. There are several wild grasses that look very similar. You could dry it for a dried arrangement if you're into that sort of thing.

Yes, wheat, probably spread by birds or birdseed.

Wheat or rye, maybe from straw, if you used any in the garden.