Across the Alt Right, it is common to encounter the idea that there is currently, in progress, a genocide taking place against white people. This is, of course, the essential data point used by an overwhelming majority in the Alt Right to create the narrative of white victimhood that fuels and justifies white nationalist identity politics.
The existence of a white genocide is established by an interpretation of the UN definition of genocide:
The most common Alt Right interpretation of this definition means that there is currently being perpetrated an on-going genocide of the white race. According to most, many influential groups in society are knowingly acting to eradicate the white race through demographic destruction over an extended period of time via the use of mass immigration.
White genocide is the idea that, on a worldwide scale, white people are undergoing a systematic genocide of their gene line and of their culture.
Since the people who promote it are generally racist idiots, "white genocide" mostly boils down to non-white or partially white people having babies. Or migrating. Or dating white people. Or existing, period.