I found this on a Chinese herb website:
"Technically, the word coriander can be used to describe the entire plant: leaves, stems, seeds, and all. However, when speaking of coriander, most people are referring to the spice produced from the seeds of the plant. The leaves of the plant are commonly called cilantro, which comes from the Spanish word for coriander."
Well, I don't know about "most people", but I call the leaves "coriander leaves", and I call the seeds "coriander seeds", and I didn't realise that English speakers used the Spanish word, but you learn something every day...