In the Seattle area, at least, this is referred to as Coriander when talking about the seed, and Cilantro when talking about the leaves. You can either reduce or increase confusion by using its Latin name, coriandrum sativum.
The seeds are small and round, about the size of a peppercorn or a BB, and light brown. The leaves are on a thin green stalk (which is chopped up along with the leaves) and brance off in little patterns, roughly roundish, about the size of a penny. The stalk and leaves make a nice garnish, as well.
A small but significant percentage of people can't stand fresh cilantro, to them it appears to have a soapy flavor. This may be a small genetic difference. Before cooking anything with cilantro for someone, make sure they're not one of these unfortunates!