Full House/Last Digit

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According to the rules of Sudoku, if a house (row, column, or box) has only one unfilled cell left, then there must also be only one digit missing from that house. Therefore, that cell can only be filled with that digit.

For example, look at row 5 in the grid below: only R5C2 is still unfilled, and 7 is the only digit missing from that row, so R5C2 must be 7:

Full House can also appear in a column or a box. For example, in column 5 of the grid below, only R8C5 is still unfilled, and 7 is the only digit missing from that column, so R8C5 must be 7:

Now look at box 6 in the grid below: only R6C8 is still unfilled, and 2 is the only digit missing from that box, so R6C8 must be 2:

Full House is a special case of Direct Naked Single. You only need to inspect one house (a row, column, or box) to determine the only possible digit for a cell, whereas a Direct Naked Single usually requires considering all three related houses of the target cell: its row, column, and box.