PLEASE EXPLAIN WHAT THIS MEANS: "Because interest income exceeded the cash-flow deficit, the combined trust funds have continued to run annual surpluses, which averaged about 4% of total expenditures from 2010 through 2020. Cash-flow deficits do not affect Social Security directly. However in 2021, the program experienced a cash-flow deficit and an annual deficit ." As shown:

Figure I.Annual Net Change in the Balance of the Combined Social Security Trust Funds, With and Without Interest Income, 1987-202 I Source: Congressional Research Service (CRS), based on data from the Social Security Administration (SSA), Office of the Chief Actuary (OCACT), "Social Security Trust Fund Data," https://www.ssa.gov/oact/STATS/ table4a3.html. Figure I.Annual Net Change in the Balance of the Combined Social Security Trust Funds, With and Without Interest Income, 1987-202 I Source: Congressional Research Service (CRS), based on data from the Social Security Administration (SSA), Office of the Chief Actuary (OCACT), "Social Security Trust Fund Data," https://www.ssa.gov/oact/STATS/ table4a3.html