Cilantro (US) or coriander leaves are an aromatic herb from the coriander plant used in the cuisines of the Mediterranean, Africa, the Middle East, Central Asia, China, South and Southeast Asia, Texas, and Latin America.
While the leaf is a herb, the ground dried fruit is also a spice used in cooking and in this case the term coriander is used even in the US.
(thanks to WikiMedia Commons for the images)