The balance of forces that keeps a star from collapsing is called hydrostatic equilibrium.

Here's how it works:

* Gravity: The immense mass of a star creates a powerful inward force of gravity that pulls all the star's material towards its center.

* Internal Pressure: Nuclear fusion reactions in the star's core produce a tremendous outward pressure. This pressure is what pushes outward against gravity.

Hydrostatic equilibrium is the state where these two opposing forces are perfectly balanced. This balance is crucial for a star's stability. If the outward pressure from nuclear fusion is greater than gravity, the star will expand. Conversely, if gravity is stronger than the internal pressure, the star will contract.

This delicate balance is what determines a star's lifetime and its eventual fate.