You searched for:
“zero age main sequence”
The point on the Hertzsprung-Russell diagram occupied by a star that has a core temperature high enough for nuclear reactions: The Zero Age Main Sequence is a major group of stars on a Hertzsprung-Russell diagram by a practically uniform band of brightness and surface temperatures that become greater and greater.
This entry is located in the following unit:
Astronomy and related astronomical terms
(page 28)