
Unit 

In Sudoku a unit is one of four things:
Row
Column
Box
Cell
By basic definition, a unit is a set of candidates of which only one can be true.
For a row, column or box, a unit is comprised of only one number. For instance, all the 3's in a column are a unit, and all the 4's in that column are a different unit. For a cell, a unit is comprised of all the numbers or candidates within that cell. For instance, if a cell can be a 1, 2 or 7, all those numbers comprise a unit because only one can be true.
Often you'll see the term 'share a unit.' If there are four 3's in a row, then each 3 shares a unit with every other 3. If there are more than two values in a unit, not only do they share a unit with eachother, but they are also weakly connected. If, instead, there are only 2, then they are both weakly and strongly connected.






