When a candidate number within a block is only in one line, the number can't be within another block in the same line.

In the example, a certain number fits only in the red cells of the block, which are all in the same line so the number can't be in the green cell. Which number comes in the green cell?

Locked number in line

If a candidate is in a line within one block only, it can't be elsewhere in that block.

In the example, a certain number fits only in the red cells of the line, which are all in the same block so the number can't be in the green cell. Which number is left alone in the green cell?

Naked pair

When exactly two candidate numbers are in exactly two cells on a line or block, the numbers can't be in any other cell on the same line or block.

In the example, the red cells each have exactly two candidate numbers, so the numbers can only be in these cells. Once the candidates are eliminated, which cell within the block has a single possible number?

Medium techniques look quite similar. They also occur often in the same puzzles. For example, "Naked pair" technique can be applied to the Sudoku of "Number Locked in Line".