Every year, the Budget is presented before Parliament by the Union finance minister. During the speech, the funds allocated for various jobs and activities and ministries are laid out. These numbers are called Budget estimates. For example, if the government sets Rs 1,000 crore aside for defence, then Rs 1,000 crore will the Budget estimate for defence for the given financial year.
One thing to note here is that these estimates are not exact numbers or the final commitment by the government to any particular sector. These are just estimates of the extent of expenditure the government is willing to go for. The government later gives a revised estimate of how much is possible for it to extend to the said sector. The revised estimates and budget estimates may vary, but the difference may not be huge. The actuals are the numbers that represent the real amount extended by the government to the sector concerned.
Budget estimates represent the government's wishes and ambitions. Revised estimates show how the expenditure is likely to pan out. Actuals give the real number for how much was really extended.