Linda,
On our discussions with Willis Lamb, he got the Nobel Prize for looking at the atomic structure of the hydrogen atom, the simplest atom (element) in the Universe. The 2s, 2p shells are orbital paths or rings like the classic Bohr atom. Envision it like the paths of the planets (electrons) in our solar system that travel in rings around the sun (nucleus). When the electrons are excited, they jump to outer orbital shells. When they jump back down, they emit energy as a photon (light) or some other means. The time it takes for this electron to return to its normal (unexcited) state is what this term means. While the atom is excited before the energy transfer back to a lower state, one could manipulate the atom with magnetic fields as the electron is farther from the nucleus. The electron could be ripped away from the nucleus, creating an ion. This also can expose the nucleus from the shielding of the electron (for hydrogen). Once the nucleus is exposed, you could add more protons, neutrons, and electrons and transmute the hydrogen atom into any element. Or rip apart the nucleus and disintegrate the atom entirely.
Hope this explanation is clear. My 2 cents worth...