Mirrored from Sudopedia, the Free Sudoku Reference Guide
A weak link exists between any 2 candidates that cannot be true (i.e. part of the solution) at the same time. These 2 candidates can either represent 2 different digits in a single cell or represent the same digit in a house.
When the 2 candidates are the only 2 candidates left in the cell or unit, they have a strong link rather than a weak link.
For the weakly linked candidates named A and B, we can make the following deductions: