What is the ninth stream of the "lower ninth stream" that we usually talk about?

In feudal society, people divided the "nine streams" into three types: upper, middle and lower.

"Shangjiuliu" is: first-class Buddha, second-class immortal, third-class emperor, fourth-class official, fifth-class member, sixth-class guest, seventh-class burning, eighth-class manor. Among them, "guest" refers to businessman, "little" refers to boiler (brewer) and "pawn" refers to pawnshop.

"Zhong Jiuliu" is a first-class doctor, a second-class doctor, a third-class expert, a fourth-class critic, a fifth-class painter, a sixth-class worker, seven monks, eight masters and nine chess players. Among them, "Feng Jian" is a master of Yin and Yang who looks at Feng Shui, and "Pi" is a fortune teller who approves eight characters.

The "dirty tricks" are: a pedicure, a haircut, three shifts of oil and six hand blows. Among them, "Ban" is the head of the squad, "Grease" refers to the restaurant owner, and "Ba" is a Jianghu artist!