Medical
Research in the late 20th century led to a growing medical consensus that diverse intersex bodies are normal, but relatively rare, forms of human biology. Clinician and researcher Milton Diamond stresses the importance of care in the selection of language related to intersex people:

Foremost, we advocate use of the terms "typical", "usual", or "most frequent" where it is more common to use the term "normal." When possible avoid expressions like maldeveloped or undeveloped, errors of development, defective genitals, abnormal, or mistakes of nature. Emphasize that all of these conditions are biologically understandable while they are statistically uncommon. Medical classifications
Sexual differentiation
The common pathway of sexual differentiation, where a productive human female has an XX chromosome pair, and a productive male has an XY pair, is relevant to the development of intersex conditions. During fertilization, the sperm adds either an X (female) or a Y (male) chromosome to the X in the ovum. This determines the genetic sex of the embryo. During the first weeks of development, genetic male and female fetuses are "anatomically indistinguishable", with primitive gonads beginning to develop during approximately the sixth week of gestation. The gonads, in a bipotential state, may develop into either testes (the male gonads) or ovaries (the female gonads), depending on the consequent events. Up until and including the seventh week, genetically female and genetically male fetuses appear identical. At around eight weeks of gestation, the gonads of an XY embryo differentiate into functional testes, secreting testosterone.
Intersex organizations have also issued statements about human rights violations, including the 2013 Malta declaration of the third International Intersex Forum. In 2011, Christiane Völling became the first intersex person known to have successfully sued for damages in a case brought for non-consensual surgical intervention. In April 2015, Malta became the first country to outlaw non-consensual medical interventions to modify sex anatomy, including that of intersex people. Terminology
There is no clear consensus definition of intersex and no clear delineation of which specific conditions qualify an individual as intersex. The World Health Organizations International Classification of Diseases (ICD), the American Psychiatric Associations Diagnostic and Statistical Manual of Mental Disorders (DSM), and many medical journals classify intersex traits or conditions among disorders of sex development (DSD).A common adjective for people with disorders of sex development (DSD) is "intersex". Etymology and definitions
In 1917, Richard Goldschmidt created the term "intersexuality" to refer to a variety of physical sex ambiguities. However, according to The SAGE Encyclopedia of LGBTQ Studies, it wasnt until Anne Fausto Sterling published her article "The Five Sexes: Why Male and Female Are Not Enough" in 1993 that the term reached popularity. According to the UN Office of the High Commissioner for Human Rights:

Intersex people are born with sex characteristics (including genitals, gonads and chromosome patterns) that do not fit typical binary notions of male or female bodies. Intersex is an umbrella term used to describe a wide range of natural bodily variations.