The Cayenne pepper is a rather hot chile pepper 2 -3 " long. It is most commonly used "ground" for flavoring various recipes including sauces, soups and stews. When you purchase chile pepper flakes they are typically from the cayenne pepper. Many bottled hot sauces use cayenne for extra heat. On a heat scale of 1 -10 this pepper is an 8.
The ground pepper is a standard grocery store item.