The biological state of having: 1) female or male genitalia (vulva, labia, clitoris, and vagina for females; penis and testicles for males); 2) female or male chromosomes (XX for females; XY for males); and 3) female or male hormones (estrogen and progesterone for females; testosterone for males); perhaps one in 2,000 babies is born with the biological characteristics of both sexes or of neither sex entirely (see intersex); see also gender and gender identity which are different than biological sex
This can be considered as our "packaging and is determined by our chromosomes (XX for females, XY for males); our hormones (estrogen and progesterone for females, testosterone for males); and our internal and external genitalia (vulva, clitoris, vagina for females, penis and testicles for males). About 4% of the population can be defined as "intersexuals born with biological aspects of both sexes to varying degrees. Therefore, in actuality, there are more than two sexes.
Being male or female, as determined by chromosomes, and body chemistry.