Boil vs cyst. A "boil" is simply a skin abscess where a bacterial infection has caused a collection of pus. The pus needs to be removed/drained. A cyst is usually the result of a blocked skin pore. The cyst material is usually the normally sloughed off skin cells that cannot simply float away. The collect within the cyst. Cysts do not always need to be treated unless they continue to grow get infected.
Infection. A cyst is a fluid collection that is not infected. An abscess (boil) is a tender mass generally surrounded by a colored area from pink to deep red. Abscesses are often easy to feel by touching. The middle of an abscess is full of pus and debris. http://www.webmd.com/a-to-z-guides/abscess#1.