United Nations Genocide Convention 1948:
Genocide is any of five "acts committed with intent to destroy, in whole or in part, a national, ethnical, racial or religious group". These five acts were: killing members of the group, causing them serious bodily or mental harm, imposing living conditions intended to destroy the group, preventing births, and forcibly transferring children out of the group. Victims are targeted because of their real or perceived membership of a group, not randomly.
Israel's current Gaza offensive satisfies all 5 criteria.