Social grading.

Grade	Social class	Chief income earner's occupation
A	upper middle class	Higher managerial, administrative or professional
B	middle class	Intermediate managerial, administrative or professional
C1	lower middle class	Supervisory or clerical and junior managerial, administrative or professional
C2	skilled working class	Skilled manual workers
D	working class	Semi and unskilled manual workers
E	non working	Casual or lowest grade workers, pensioners, and others who depend on the welfare state for their income,

This table shows how media networks class their audiences into different categories, they do this for many reasons one being because the people aren't all in the same group, so they enthersise people are in different classes.