What was meant by the term 'Imperialism', as a cause for World War I?

Imperialism is the policy by which a powerful nation establishes control over another country — by political pressure, economic penetration or outright war — and holds it as a COLONY, exploiting its raw materials, markets and people for its own benefit.

As a cause of the First World War, the industrial powers of Europe competed fiercely for colonies in Africa and Asia. Germany, a late entrant, resented the vast empires already held by Britain and France and demanded her "place in the sun", and this rivalry created the bitterness that led to war.

Two marks, so give the definition AND the link to the war — the question says "as a cause for World War I", so a definition alone earns half. The phrase "a place in the sun" is Kaiser Wilhelm II’s and is worth quoting; it captures the German grievance in five words. The other underlying causes to keep distinct: aggressive nationalism, the armament race and the system of alliances.