Usually, masculinity is defined in terms of various lists of traits or characteristics. However, there is no authoritative list of such traits.
The idea of ‘masculinity’ does not exist except in contrast with ‘femininity.’ Cultures that do not treat men and women as polarized opposites do not have a concept of masculinity in the way it is used in modern American and European cultures.
Using ‘masculinity’ and ‘femininity’ came with the industrial revolution and the middle-class notion that men live in the world ‘outside’ and women live in the ‘inside’ world. The heightened gender differentiation of this era morphed into biologically determined, timeless truths about masculinity.
While men continue to struggle with how masculine they are, women are not struggling with their femininity. Women are blowing up the whole gender thing. Women are looking to enter the ‘outside’ world of men. They want men to enter their ‘inside’ world, to share power and authority inside and outside. This is the crisis that threatens the idea of masculinity you see expressed in the protest of such men as [Jordan] Peterson and the ‘incels.’
The crisis of masculinity is, thus, a crisis of gender. To talk about ‘masculinity’ and ‘femininity’ is to talk about gender relationships—the patterns by which men and women engage with each other dictated by the idea that they belong to different spheres of life.