Common meaning:

The practical advantages of being thin.

Hidden meaning of the Equity religion: 

All thin people experience systemic advantages over fat people.

Discussion:

The Equity believers claim that thin people have systemic advantages over fat people and that the thin people are all oppressing them and causing them violence.

It is true that in this world, there are many things that have been designed for people that are of a typical size or, as the Equityists would say, thin. This does not mean they were designed to oppress fat people, just that they were designed for the average person’s size and not all extremes can be accounted for. The price we pay for being part of a society is that things have to be designed for normal or average size.

The Equityists claim that Western society does not design things due to physical limitations but only because thin people hate fat people. They show this by the size of seats they create for airplanes and the jokes they say to make fun of fat people. All of this is causing violence to those who are fat. 

You will notice the typical Equity trick of calling something violent when it is clearly not.