The S-orbital is a type of atomic orbital that can hold a maximum of two electrons. It is spherical in shape and is the simplest of all orbitals. S-orbitals are found in all energy levels, starting from the first level, where the 1s orbital is located. In the context of the quantum mechanical model of the atom, S-orbitals play a crucial role in determining the electron configuration of elements. They are essential for understanding chemical bonding and the behavior of atoms in periodic table trends.