Biological sex refers to the physical and physiological differences between male and female organisms, primarily determined by their reproductive systems and secondary sexual characteristics. In humans, biological sex is typically categorized as male or female based on the presence of specific chromosomes, such as XY for males and XX for females. These differences include reproductive organs, such as testes in males and ovaries in females, as well as other traits like body structure and hormone levels. While biological sex is often seen as binary, some individuals may have intersex variations, which can involve atypical combinations of chromosomes, hormones, or anatomy.