Article 7 of the Rome Statute of the International Criminal Court defines crimes against humanity as:
Crimes against humanity
1. For the purpose of this Statute, ‘crime against humanity’ means any of the following acts when committed as part of a widespread or systematic attack directed against any civilian population, with knowledge of the attack:
• Deportation or forcible transfer of population;
• Imprisonment or other severe deprivation of physical liberty in violation of fundamental rules of international law;
• Rape, sexual slavery, enforced prostitution, forced pregnancy, enforced sterilization, or any other form of sexual violence of comparable gravity;
• Persecution against any identifiable group or collectivity on political, racial, national, ethnic, cultural, religious, gender as defined in paragraph 3, or other grounds that are universally recognized as impermissible under international law, in connection with any act referred to in this paragraph or any crime within the jurisdiction of the Court;
• Enforced disappearance of persons;
• The crime of apartheid;
• Other inhumane acts of a similar character intentionally causing great suffering, or serious injury to body or to mental or physical health.
The crime of apartheid is defined as:
2. (h) The ‘crime of apartheid’ means inhumane acts of a character similar to those referred to in paragraph 1, committed in the context of an institutionalised regime of systematic oppression and domination by one racial group over any other racial group or groups and committed with the intention of maintaining that regime.
Read the Rome Statute on the UN site