What is the term for a fully formed star?

A fully formed star is referred to as a main sequence star, which is the phase most stars, including our Sun, spend the majority of their life. During this stage, a star has reached a stable state where nuclear fusion occurs in its core, converting hydrogen into helium and releasing a significant amount of energy in the form of light and heat. This phase is marked by a balance between the gravitational forces trying to collapse the star and the outward pressure from nuclear fusion.

In the main sequence stage, stars are categorized based on their mass and luminosity, ranging from small, cooler stars to massive, hot stars, each exhibiting specific characteristics. This stage is crucial in stellar evolution, representing the peak of a star's lifespan where it shines brightly and remains stable, contrasting with the other terms mentioned, which refer to different stages before or after the main sequence phase.