As we've learned, Gender and Biological Sex are not the same thing. Gender involves both expression and identity, which may very from person to person!
Gender Identity:
This is one's concept of self as male, female, both, or neither. One's gender identity can be the same or different than their assigned sex at birth. Many adopt a gender that matches their physical sex; however, for some it can be completely different.
Gender Expression:
This refers to the way that people communicate their gender identity through appearence and communication. This can be done through:
Behavior, clothing, haircut, voice, et cetera...
It is important not to assign gender to someone based on their appearence, as you could assume incorrectly and offend them. Clothing you may deem feminine or masculine may not be regarded as such by someone else.
People who do not identify with thier assigned birth sex prefer to express themselves with their gender identity.
Many parents are starting to raise their children as gender neutral. This means that they are bringing up their kids in a an environment that doesn't force them to wear certain colors, play with specific toys, or dress up in clothes that are gender specific.

As time progresses, feminity and masculinity and becoming blurred, and the ultimate mixture the of the two is called "androgyny" (female and male characteristics). Many famous celebrities and artists are known for their androgyny.
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