zero-age main sequence

Zero-age main sequence (ZAMS, also called standard main sequence) is a term for the main-sequence relationship (absolute magnitude to effective temperature) specifically for those stars that have just begun hydrogen fusion. As plotted on an H-R diagram, it is a subset of the main sequence. The term terminal-age main sequence (TAMS) is also used, to indicate a star that is ceasing hydrogen fusion in the core, ready to evolve into its post-main-sequence stages.