What state defines a stable main-sequence star like the Sun?

Answer

A state where outward thermal pressure exactly balances the inward crush of gravity

Hydrostatic equilibrium is the crucial balance achieved by stable stars where the immense outward pressure generated by core fusion perfectly counters the constant inward pull of the star's own mass.

What state defines a stable main-sequence star like the Sun?
astronomyforcegravitystar formationinterstellar cloud