A Chinese phrase, popularized in modern times by Mao Zedong, used to describe something that projects great threat or power but is ultimately weak or ineffective in practice.

The atom bomb is a paper tiger which the U.S. reactionaries use to scare people. It looks terrible, but in fact it isn’t. Of course, the atom bomb is a weapon of mass slaughter, but the outcome of a war is decided by the people, not by one or two new types of weapon. All reactionaries are paper tigers. In appearance, the reactionaries are terrifying, but in reality they are not so powerful. – Mao Zedong

From ‘Selected Works of Mao Tse-Tung’