What does white horse grass mean?

White horse Cao refers to Guan Yu helping Cao Cao solve the siege of white horse. In the fifth year of Jian 'an, Cao Gong made an expedition to the east, and the first master ran Yuan Shao. Cao Gong's bird feather came home and worshipped him as a partial general. The ceremony was very grand. Shao sent Yan Liang, a general, to lead the Eastern County to the White Horse, and Tsao Gong made Zhang Liao and Yu as pioneers. Feather saw the cover of a good man, stabbed him in the crowd on horseback, beheaded him, and let go of what the generals could not do, thus solving the problem of Bai Mawei. Cao Gong named his feather the Pavilion Hou of Hanshou. Tso was a strong man at the beginning, but he didn't want to stay in his mind for too long. He said to Zhang Liao, "Please try to ask him with emotion." Liao asked Yu, who sighed, "I am well aware of Cao Gong's kindness to me, but I was sworn to death by General Liu's kindness and I can't carry it back. After all, I won't stay. I'll report to Cao Gong immediately. " Liao Yiyu reported Cao Gong and Cao Gongyi. When Yu killed Yan Liang, Zuo Zongtang knew he would go and gave him a big reward. Feather thanked him, said goodbye to Shu En, and ran to Yuan Jun first. When the left and right wanted to chase him, Cao Gong said, "Each is his own master, so don't chase him."