Definitions of Masculinity and Femininity (from What's the Difference? by John Piper):

MASCULINITY

At the heart of mature masculinity is a sense of benevolent responsibility to lead, provide for and protect women in ways appropriate to a man's differing relationships.

FEMININITY

At the heart of mature femininity is a freeing disposition to affirm, receive and nurture strength and leadership from worthy men in ways appropriate to a woman's differing relationships.

In What's the Difference?, John Piper goes on to carefully and insightfully break down each part of these two definitions to give a fuller understanding of Biblical masculinity and femininity.

I am currently reading What's the Difference?, but the small booklet is actually a chapter taken from Recovering Biblical Manhood and Womanhood, coauthored by John Piper and Wayne Grudem.