Full house
A full house is a row, column or section with one empty cell left. Since all other cells have been filled, there is only one possible digit that can be placed in that empty cell.
Last digit
Each digit can be placed 9 times in a grid. When a digit already have been placed 8 times, there is only one cell where that last digit can be placed. This digit is then a hidden single in all of its houses.
Naked single
A naked single is the last remaining candidate in a cell. It can easily be spotted by using pencil marks, or by inspecting the cells peers. If no other digits can be placed in that cell, then the remaining digit is the only possible candidate.
In this puzzle, the naked singles in row 3 have been marked. As there are no other candidates in those cells, the digits can be placed in those cells
Hidden single
A hidden single is a last remaining candidate for a specific digit in a row, column or section. There can be other candidates in that cell, but for that specific digit there is no other cell it can be placed.
This puzzle contains 2 hidden singles in column 1.
No other cell in box 4 can contain the digit 2, therefore the only place it can be put is in cell r4c1. The same applies with the digit 5 in box 7.
There are more hidden singles in the puzzle, can you find them?