What is the difference between Gender and Sex?

Sex and gender, though appear to be one and same are very different from one another. Sex is a biological difference between men and women, whereas, gender is a socially constructed difference. Sex is something that cannot be changed by society, whereas, gender is the role assigned to the individual and is a socially constructed norm. An individual is born as male or female, but it is the society that identifies them as masculine and feminine on the basis of their expectations.