I am referring to the Maoist concept of social imperialism of the USSR, which I tend to agree with.

I am not talking about capitalist financial imperialism, this allegation being well refuted by Castro:

How could the Soviet Union be classified as imperialist? Where are its monopolist enterprises? What is its participation in multinational companies? What industries, what mines, what petroleum deposits does it own in the underdeveloped world? What worker is exploited in any country of Asia, Africa or Latin America by Soviet capital? The economic cooperation which the Soviet Union is offering Cuba and many other countries did not come from the sweat and the sacrifice of exploited workers of other peoples, but from the sweat and effort of Soviet workers

Edit: Castro’s refutation is also a great explanation, of why I would classify today’s PRC as regularly imperialist, even if not to the degree of the USA/EU etc.