The region of space in which an electron in an atom is most likely to be found is called an atomic orbital.

Orbitals are designated by three quantum numbers, n, l, and m_l, that describe the electron shell, subshell and orientation in space.

Each orbital in an atom can contain 2 electrons with opposite spins.

The orbitals are shown below: (images from Zumdahl, Chemistry, 3rd. ed.)