A diamond (also known as a “blood diamond”) that is mined to fund violent conflict and/or civil war against a legitimate government. Such mining is often linked to dire human rights abuses. Blood diamonds have originated in many countries in Africa. The amount of conflict diamonds (as a percentage of world diamond production) has fallen dramatically, currently resting at about 4 percent according to international tracking methods as part of the Kimberley Process. In countries where legislation is in place prohibiting the sale of conflict diamonds, such as in the United States, the percentages are much lower.
See the FAQ: How can I avoid conflict diamonds?