Ceylon Cinnamon is also called Sweet or True cinnamon. Its mainly grown in Sri Lanka and Southern India, but also in places like Madagascar and the Carribean. It's sweeter, not as hot, and mainly used in Europeran (French) cuisine, Sri Lankan cuisine, and health food applications.
An older botanical name for this kind of Cinnamon is Cinnamomum zeylanicum.
Volatile Oil ~ You'll notice that our cassia listings have a "Volatile Oil" specification on them. The volatile oil is what makes a cassia stand out. Most cassias sold comercially will have anywhere from 1.5 to 2.8 percent - this is a very good way to classify the character and intensity that the spice will bring. True Cinnamon (i.e. all the items in this category) doesn't have this specification.