He means the US empire and before it the British, Spanish and Portuguese ones with colonialism, slavery/neo-slavery and exploitation as the main mindset that is organized, institutionalized and culturally absorbed.

Indi did elaborate once, though not perfectly, on what he meant by ‘white empire’ and said that it is not about the whiteness of the skin. There are counter-examples both ways of which you declare yourself to be one. I prefer calling it the US empire though there are non-US citizens ruling at the highest level and many ‘mericans who are disenfranchised.

However, it is important to have a designation for this organized, institutionalized and culturally absorbed abstract entity having a historical continuity in order to better understand its historical and current dynamics. No model of reality and no word perfectly reflects reality but we need words to reason about things. ‘White empire’ has some strengths and some weaknesses while US empire has the weakness of omitting the historical context.

Whatever you call it, call it, because the first step of enslavement or freedom is the naming of things, or as Orwell indicated, failing to do so.