All hops have both aromatic and bittering properties. However, hops that have high levels of alpha acids (over 10%) are considered as bittering because their aromas often do not match the profile that the brewer wishes to achieve.
The cone is the female flower of the hop plant. Once it is dried, it can be used as is in the brewing process. Pellets are formed from of dried hop cone powder, and are more practical to use and store.