Zero-age Main Sequence (zams)

Region on the Hertzsprung-Russell diagram, as predicted by theoretical models, where stars are located at the onset of nuclear hydrogen burning in their cores. These stars are new additions to the main sequence, a place where they will spend about 90% of their lives and maintain remarkably stable luminosities. After this time, they evolve off the ZAMS to the upper right of the main sequence to become red giant or supergiant stars.


Image source: http://www.peripatus.gen.nz/Astronomy/HerRusDia.html.