Yan Gu refers to the vigorous fonts of () and (), and is also used to praise others' () works for their sense of urgency.

"Yan" refers to Yan Zhenqing, and "Liu" refers to Liu Gongquan, four famous regular script writers in the history of ancient calligraphy in China: Yan Zhenqing in Tang Dynasty, Liu Gongquan, Ou Yangxun and Zhao Mengfu in Yuan Dynasty. Yan and Liu occupy half of the seats. "Yan Liu Jin Gu" means that their styles are as strong and different as tendons and bones.