Imperialism is the practice, theory or attitude of maintaining or extending power over foreign nations, particularly through expansionism, employing not only hard power (economic and military power), but also soft power (cultural and diplomatic power). Imperialism focuses on establishing or maintaining hegemony and a more or less formal empire.
Russia (and the Soviet Union) has had multiple rounds of imperialism throughout its history. Slicing bits off Ukraine and its continued occupation of parts of Georgia in the modern era certain counts as expansionism. It also exercises cultural power by using state controlled Russian-language media to influence both domestic and foreign populations.