A Social Accounting Matrix is a square matrix in which each account is represented by a row and a column. It provides a comprehensive picture of the economic transactions of an economy. Each cell shows the payment from the account of its column to the account of its row. Thus, the incomes of an account appear along its row and its expenditures along its column. For each account in the SAM, total revenue (row total) should be equal to total expenditure (column total).

Source: un.org