From the Background: "The Future Years Defense Program (FYDP) is a projection of the forces, resources, and programs to support Department of Defense (DOD) operations. The FYDP is compiled every year and typically completed during the programming phase of the Planning, Programming, Budgeting, and Execution (PPBE) process. The projection is updated during the budgeting phase to reflect DOD's final funding decisions presented in the annual President's budget request. The FYDP reflects the planned allocation of DOD resources to major strategic efforts over a multiyear period. According to the department's Future Years Defense Program (FYDP) Structure Handbook, the FYDP is intended in part to link DOD's internal review structure for programs with Congress's review structure for resources, including funding. The FYDP projects DOD funding, manpower, and force structure needs over a five-year period. The projection is typically depicted with defense resources for the two previous fiscal years and force structure estimates for the three subsequent fiscal years."
CRS In Focus, IF10831
Congressional Research Service: https://crsreports.congress.gov/