I’m Confused on What Are M and v Shape Hairlines, Help Me Understand!

The V-shaped hairline is the typical mature male hairline. I have written about hairlines here:https://newhair.com/wp-content/uploads/2018/11/phenotype-article-published.pdf which covers the different hairline shapes and how you get them as you get older.  This link shows examples of both types of hairlines with some good photos: https://baldingblog.com/juvenile-vs-mature-hairline-am-i-going-bald-with-photos/