Perhaps you are referring to main sequence stars. These are the most common type of star, and their main activity is nuclear fusion.
Here's a breakdown:
* Main sequence stars: These stars are fusing hydrogen into helium in their core. This process releases immense energy, which makes the star shine and provides the outward pressure that balances the inward force of gravity.
* Nuclear fusion: The process of combining atomic nuclei to form heavier nuclei. In main sequence stars, hydrogen atoms fuse to form helium.
Let me know if you meant something else, and I can help clarify!