Capsicum is a special type of pepper. The red and green bell peppers that are considered a vegetable and are not hot are considered to be a capsicum. Chili peppers are hot usually or sweet. They are considered to be peppers and are long and thin in size. They may be the same colors as the bell peppers in yellow, red and green, but they are a different size. Bell peppers or capsicum are rounded in shape.
Their skin is thick and shiny. Another main difference is the taste. Bell peppers are neither hot nor sweet, but the chili peppers are either one or the other. They are also used differently in recipes because bell peppers are used as a vegetable and peppers are used for flavor.
Chili peppers are actually a capsicum, as capsicum is another word for pepper and encompasses the entire genus. A genus is basically a category of similar plants or animals that can be further divided by their characteristics. The capsicum genus includes all colors of bell peppers, banana peppers, jalapenos, habanero, cayenne, and many others.
Some of these peppers are ranked highly in terms of heat, other have no heat but plenty of flavor. Although in the United States, we refer to these plants as "peppers," in other areas of the world they are simply called capsicums. Chili peppers can further be divided into mild or spicy, with many different levels of spice.