An orbital is defined as a region of the most probable location of
an electron
a neutron
a nucleus
a proton

An electron
An orbital is defined as a region of the most probable location of an electron. Nucleus is the center and core of an atom, where in the neutron and proton is said to be found. Electrons, now are the orbiting bodies or entities around these nucleus of an atom. In analogy, similarly, an atom is like our solar system where sun is simple the nucleus and the planets are the supposed electrons.