What does a third-rate person mean?

In feudal society, people were divided into three classes: three, six and nine. It was Ban Gu, a historian of the Eastern Han Dynasty, who divided the ancient and modern characters into "nine-grade list" in "Hanshu Ancient and Modern Characters List", which was divided into upper, middle and lower grades. Generally speaking, the so-called "3699" is to distinguish the categories and levels of everything in the world and even everything in the universe. Three religions and nine streams, three religions refer to Confucianism, Buddhism and Taoism. Nine streams are divided into upper, middle, lower, third and third natural numbers, and three or three get nine. Shangjiuliu refers to Buddha, heaven, earth, kings, officials, cabinet elders, prime ministers, scholars, juren and Xie Yuan. Zhong Jiuliu refers to literati, doctors, painters, shadow play, playing and singing, floating gold, monks, Taoist priests and artists. Dirty people refer to stage actors, stage musicians, circus, floating piles, pools, people who rub their backs, repair keys and some prostitutes. Therefore, if you want to improve your status in a hierarchical feudal society, you must change careers, otherwise it will be difficult to achieve your ideal goal.