What is the difference between sex and gender?

Well gender means if ur male or female example u see a thing on a dmv paper it says gender then it say male or femal if that was justin beiber it would be female hahaha an sex..... Oh boy its when a male an a female colide in a way an they have a baby of a random gender an u know the rest kiara daly

Sometimes there is no different sex can also refer to gender or it can mean intercourse, its a double enetendre

Well if ur talking if ur male or female than theres not a difference

The difference between genders is very important when I am having sex.

Quite simply put sex refers to the biological orientation of the individuals reproduction organ while may refer to the mental disposition of the person as in the behavioural, mental and physical aspects of the individual. In sociology 'sex' refers to nature while 'gender' refers to nurture.

So if you say your Gender in undetermined but your Sex is actually female then you could simply mean your not that feminine. Often times the two are confused because there is very little difference between them.

Sex have only three letters and gender have six , poor poor sex ?

Both are words which can be used for same as well as different  meaning