Cilantro is known as coriander in English speaking countries outside of the US and it refers to the entire plant. That's why you can visit IHateCoriander.com and it redirects you here, to IHateCilantro.com. As far as I know, the English word cilantro is really only used in the United States.
To most people in America coriander is just the seed and cilantro is the leaf. But why does it have a different name?
Cilantro is the Spanish word for coriander (check it out) and the herb is commonly used in Mexican food. Most likely, the Spanish word is used in America because of its proximity to Mexico. Many people of Mexican descent live here and Mexican cuisine is common.
No matter what you call it, people still hate coriander and the way coriander tastes (like soap, stinkbugs, or plastic lemon feet).
Here are some other words for cilantro:
- Coriandrum sativum (Wikipedia)
- Chinese parsley (Wikipedia)
- Mexican parsley (What's Cooking America)
- Devil weed (mostly just on IHC. e.g., by leester, twenty|one|pilots, and Sylvester :) )