Y or X are gross output measures, Y = real GDP; but for disposable income the term used is WA, or more specifically, after tax compensation (wages) of employees. YTR is transfer or non wage income.

A or AA represents household assets or net worth.

R represents an interest rate, and combined with S is a short term (3 month treasury bill), with M for mortgage rate, and A as the final letter means after tax.

K is the capital stock designated for its specific sector, D = durables and H for housing.

P represents the price index with designation for the specific sector, e.g., PCS for consumer services, etc., H for all households.

M = money, where the demand relationships are separated into MH for households and MF for firms.

POP is population. Note the Fairmodel is estimated in a per capita form this many variables are divided by POP.