Does anyone know if this is a plant or a weed?

It is ribwort plantain. It is a common weed that has holistic mecicinal uses:, mildly anti-bacterial, bitter, anti-septic, astringent, demulcent, mildly expectorant, haemostatic, diuretic.

As Em said it's Plantain. It's though to have been used for over 2000 years as a medicinal plant. It has the nickname 'Nature's Plaster' as it is so useful for promoting skin healing :)

Thank you.

A weed is only an unwanted, misplaced plant. What some people consider weeds, others consider edible, medicinal, ornamental or otherwise useful, beneficial plants. If you like it or if it serves a useful purpose for you, keep it. If not, get rid of it.