"Paper tiger" is a calque of the Chinese phrase zhǐlǎohǔ (simplified Chinese: 纸老虎; traditional Chinese: 紙老虎). The term refers to something or someone that claims or appears to be powerful or threatening but is actually ineffectual and unable to withstand challenge.
The expression became well known internationally as a slogan used by Mao Zedong, former chairman of the Chinese Communist Party and paramount leader of China, against his political opponents, particularly the United States. It has since been used in various capacities and variations to describe many other opponents and entities.