Store bought celery is Apium graveolens var. dulce, mainly eating its thick leafy stalk because its mild flavor strong stems so often can be eaten raw or cooked.
In Asian supermarkets they sell leafy celery (Chinese celery), which is Apium graveolens var. secalinum, strong aroma, thinner stalks, mainly used as flovoring herb with stalks and leafs, it can be cut to fine pieces and use re-sealable bag storing in freezer.
There is one another common seen celery only sold turnip like roots in supermarket, it is Celeriac/turnip-rooted celery (Apium graveolens var. rapaceum). Mainly use its fleshy root. Its stalks and leaves with strong aroma so often use as garnish.