Gender and sex - two words that are regularly confused.
Gender either refers to a term of grammatical classification for nouns etc., or to socially constructed personalities. If the answer to a question is masculine, feminine, or neuter, then the question is asking about gender.

Sex when used to classify (as opposed to talking about sexual intercourse) refers to the division of living things into male and female. If the answer to a question is male or female, then the question is asking about sex.
It is not difficult to comprehend this useful distinction. Basically, when you’re talking about what biological wobbly bits people have, you are talking about sex differences.

There is no reason to be unclear about the definitions. Let's refer to the OED Online:
sex, n.
Either of the two main categories (male and female) into which humans and many other living things are divided on the basis of their reproductive functions; (hence) the members of these categories viewed as a group

gender, n.
In some languages: each of the classes (typically masculine, feminine, neuter, common) of nouns and pronouns distinguished by the different inflections which they have and which they require in words syntactically associated with them;
I have also just had a look in my Minster Guide to English Usage, which agrees: "Male is always used with reference to sex, whether of human beings or other forms of life".

Male/Female = Sex
Masculine/Feminine = Gender

However, there is a widespread misuse in our society - many people talk about 'gender equality' when they mean 'sex equality'; or they ask for your 'gender' on forms, when they really mean 'sex'. Although it is a common mistake it is still a mistake. It is strange that people make this mistake when we all know that discrimination against males or females is called sexism (not 'genderism').

Even the World Health Organization realise that the terms are commonly misused, and discuss the differences on their website.

Recently I was annoyed to see a survey form being developed by a university, in which students were asked for their 'gender' when the options were male and female and the question was really about sex. I pointed out the error but it was kept. The reasons given were that:
a) because the term is used incorrectly elsewhere so people expect it; and
b) because the word 'sex' might upset people.

Both are ridiculous. The latter brings to mind the idea of moral guardians who must police language lest seeing the word 'sex' might remind people of its other meaning and lead them to an apoplectic swoon, or to uncontrollably partake in said act... Surely the Victorian period is over and we no longer have to cover shapely piano or table legs because of prudishness? Apparently not.

If you really can't stand to use the correct term then just ask the question this way:
Are you - Male?Female?

I was pleased to see that April's UK census used the correct word, sex.



The sign-up screen for the US version of Facebook uses the correct term, sex...

... but the UK Facebook sign-up screen uses the incorrect term, gender (March 2011).
Inconsistency even within a single company.

The UK Home Office use the correct term, sex. (January 2012)

The UK Jobcentre uses the correct term, sex. (May 2015)