Imperialism is the highest stage of capitalism according to those of us following Lenin and his book by the title of "Imperialism: The Highest Stage of Capitalism."
Imperialism is characterized by monopoly corporations and the compulsion to export capital abroad (for higher profits). Unlike capitalism in earlier stages, in the imperialist stage, capitalism has no more progress to bring the world, only the continuous threat of extinction through world war and environmental catastrophe.
Historically, the term before Lenin often referred to colonialism (the direct rule of other countries by a mother country) or conquest of other countries. Lenin also meant for the term to continue that connotation. According to Lenin, the countries with the highest stage of capitalism (imperialist countries of Europe and North Amerika) would periodically re-divide the world through world war. World War today is only the political extension of the economics of competition inherent within capitalism.
An imperialist is a member of the ruling class in a society with the highest stage of capitalism. Through their control of the means of production either through ownership or power in government, imperialists would not have to work a day in their lives if they did not want to.
"Imperialism" is the word that the petty-bourgeoisie chastises us the most for using. It is grating and unpleasant to the petty-bourgeoisie proud of its country.
Imperialism is the cause of contemporary militarism. It is impossible to understand communists today without understanding the interventions and national conflicts caused by imperialism.
Examples of imperialist countries are the united $tates, Japan, Germany, England, France, Italy, Belgium, the Netherlands, Luxembourg and Switzerland. We also include Russia and possibly China, though these last two have definitive majorities that are exploited, not exploiters.
Examples of imperialists are Bush, Cheney, Rockefeller, Bill Gates, Lee Iacocca, Mitterand, DeGaulle, Chirac and Tony Blair.
Buy Lenin's book on imperialism, perhaps his most influential book