What is the difference between a nuclear bomb and an atom bomb?
An atom bomb is a type of nuclear bomb. A nuclear bomb is the most general term for a weapon that utilizes nuclear chemical reactions as its power source. There are two major types of nuclear bombs, atom bombs and hydrogen bombs.
Atom bombs are the original nuclear bombs and exclusively utilize nuclear fission reactions for energy. Fission is the process of the breaking down of the nucleus of a radioactive atom into smaller parts, thus releasing energy. Uranium and plutonium are the classic examples.
Hydrogen bombs utilize a combination of fission and fusion reactions to generate energy. Nuclear fusion is the binding together of two smaller nuclei into a larger one (hydrogen into helium, for example).