In France, the word céleri properly relates to a number of plants which have a common ancestor and which have celery-like flavour. These include what the British call celery, the swollen root vegetable celeriac, and lovage. This is much as we might called any number of plants 'cabbage', but might in some circumstances want to be more specific and get hold of some spring greens, or a Savoy cabbage or cavolo nero. In practice, most French would understand céleri as being what the British call celery.
