What is gender?

I feel like any time gender is brought up we are automatically talking about women or feminism. Does this mean there are no gender issues with men? In Gender and Race by Evelyn Nakano Glenn, she takes the issue one step further claiming that race is the study of men of color and gender is the study of white women. Glenn continues to say that gender provides a look into historical, cultural, and situational definitions of what it means to be and man or a woman. Thus, stating that there can be no one definition for a man or a woman? If each culture is different and each person comes from a different kind or historical background with different baggage that aides in shaping their person, then how can there be such specific "boxes" of men and women? Glenn argues that they are "never fixed", so then what would a socially constructed box of a women look like in 1920, 1950, 1990, 2010, or even 2050?

How would they change? Would there be anything that remained the same throughout those periods? Moreover, what would a socially constructed box of a man look like in those periods, would his profile change drastically over time or would it hold more constant theme?

I would argue that the "box" of a female has made more drastic leaps - for better and worse- than the male. However, that could just be my own constructed version of gender taking over.