Final answer:
The concept that refers to the biological distinction between males and females is 'sex', which includes both primary and secondary sex characteristics.
Step-by-step explanation:
The concept that refers to the biological distinction between males and females is sex. Sex is a biological term that denotes the presence of physical or physiological differences between males and females, encompassing primary sex characteristics such as the reproductive system, as well as secondary sex characteristics including things like height and muscularity. Whereas gender is defined by behaviors, personal traits, and social positions that society attributes to being female or male, sex refers specifically to biological aspects such as chromosomes (XX for females, XY for males), hormones, and internal and external sex organs.