Pre-Main Sequence stars refer to stars that have left the Proto-Star era but have not fused hydrogen into helium in their cores yet, therefore they are called pre-main sequence. This was made to help people learn more about stars and also to help planetball scratchers when it comes to "(letter) type star system" projects (if you know what those are). (this may or may not be for a star system project)
if you want the sources for a more broad overview and perhaps correct me for any wrong information: https://lweb.cfa.harvard.edu/~pberlind/atlas/htmls/pmsstars.html https://en.m.wikipedia.org/wiki/Pre-main-sequence_star
