Anti-communism is opposition to Communism.
As Communism supports a (worldwide) communist revolution, followed by a Communist "dictatorship of the proletariat" and in effect the persecution and elimination of other ideologies, Communism has been more or less opposed by numerous non-Communist ideologies and movement, including even far left ones.
After the creation of the Soviet Union and especially during the Cold War, anti-Communism became associated with opposition to the Soviet Union and other Communist states, especially as they supported numerous, often criminal/revolutionary Communist activities and organizations in other countries.
Anti-Communism has often been peaceful, such as criticisms of the ideology and its assumptions or criticisms of the Communist states, such as regarding the Mass killings under Communist regimes.
A less politically correct form of anti-Communism is by fascism/National Socialism, including less politically correct views on topics such as the Spanish Civil War and the Soviet offensive plans controversy, including the associated view that the National Socialist Germany's invasion of the Soviet Union prevented a planned Soviet conquest of Europe and the World.
Jews have had a complex relationship with Communism and anti-Communism, as discussed in the article on Jews and Communism.
There are cases where anti-Communism have been claimed to have caused injustices. A prominent politically correct example is "McCarthyism", with there being less politically correct views on this as discussed in the article on this topic. Other claimed examples include Operation Gladio and certain of the anti-Communist coups or military interventions during the Cold War, although there often various problems with the (leftist) politically correct descriptions of events.
In the last few decades of the 20th century the US Western Goals Foundation and its British counterpart, Western Goals were leading anti-communist organisations.