What is meant by the ground state of an atom?

Let's start by explaining that each atom in its natural state has a specific structure of its energy levels. Where the lowest energy level is called the ground state.

At this level, as long as no energy is communicated to the atom, the electron will remain in the ground state.

What does this mean?

When an atom is in its ground state, its electrons fill the lower energy orbitals completely before they begin to occupy higher energy orbitals.