From Sudopedia, the free Sudoku reference guide
Bilocal
From Sudopedia
A Bilocal Unit exists in a house where only 2 candidates are present for a particular digit.
The pair of cells containing these candidates are called a conjugate pair. The candidates themselves have a strong link, because one of them must be true.
Bilocal units are the building blocks for several solving techniques, including coloring and several types of chains and loops.
