Answer: Containment policy was intended to prevent communism from spreading beyond the Soviet Union and its allied states in Eastern Europe.
Context/details:
The policy of containment set the tone for US foreign policy by focusing on keeping communism and the Soviet Union's influence limited, rather than by trying to confront the Soviet Union directly or eliminate communism completely.
George F. Kennan recommended the policy of containment which set the tone for US involvement in world relations following World War II. Kennan was an American diplomat in Moscow after World War II. In 1946, he sent what became known as "the long telegram" of his advice about what the USA needed to do about the Union of Soviet Socialist Republics (USSR).
In those days, everyone feared an ultimate confrontation between the USA and the USSR -- that the Cold War would someday explode into a massive heated conflict between the superpowers. Kennan, in Moscow, had much foresight to see the internal problems the USSR had. He advised not pushing the conflict too much, but instead just try to "contain" the Soviet Union and wait for their system to collapse under the weight of its own problems. Kennan was right. It took almost 50 years, but eventually the communist system in the USSR fell apart. [The Union of Soviet Socialist Republics came to an end in 1991.]