Final answer:
An orbital is the space around an atom's nucleus where electrons are likely to be found, distributed within different energy levels known as electron shells, and forming a denser electron cloud near the nucleus.
Step-by-step explanation:
An orbital is the three-dimensional region in space surrounding the nucleus of an atom where there is a high probability of finding an electron. In the quantum mechanical model of the atom, these electrons do not occupy fixed paths but are distributed within regions known as electron shells. The probability density of finding an electron in a particular location forms what is often described as an electron cloud. This cloud is denser closer to the nucleus, reflecting a higher likelihood of finding an electron there. The concept of orbitals is fundamental to understanding how electrons are spatially distributed around the nucleus, which in turn helps scientists predict an atom's behavior in chemical reactions.