The term biennial budgeting refers to budgeting for a two-year period instead of the more typical annual period.
A budget covering a period of 2 years. The federal government has an annual budget, but there have been proposals to shift to a biennial budget. The 2-year period can apply to the budget presented to Congress by the President, to the budget resolution adopted by Congress, or to the frequency and period covered by appropriations acts. The Department of Defense Authorization Act, 1986, Pub. L. No. 99–145, required the Department of Defense to submit 2-year budgets beginning with the budgets for 1988 and 1989. However, to date, appropriations have been made on an annual basis.
References for Biennial Budget
CBO – Report on Biennial Budgeting (Congressional Budget Office Report) February 1988