Final answer:
Stellar equilibrium refers to the balance between the internal pressure from heat in a star's core, due to nuclear fusion, and the gravitational force caused by the star's mass. This state of balance is known as hydrostatic equilibrium, analogous to the pressure balance in an inflated balloon.
Step-by-step explanation:
The term stellar equilibrium refers to the state in which a star is stable, neither expanding nor contracting. This stability is achieved through a balance between the internal pressure caused by heat from nuclear fusion and the external force of gravity due to the star's mass, a condition known as hydrostatic equilibrium. Specifically, in the context of stellar physics, the equilibrium is maintained because the pressure from the nuclear reactions within the star's core pushing outwards is perfectly counteracted by the gravitational forces pulling inwards.
The energy generated by nuclear fusion in the core of a star like our Sun maintains this balance. As a practical example, consider an inflated balloon where the internal and external pressures balance out; similarly, a star will expand or contract until the internal pressure and external gravitational forces become equal, thus reaching equilibrium.