Mirrored from Sudopedia, the Free Sudoku Reference Guide
A vertical line containing 9 cells.
Together, the columns form one of the 3 main divisions of the grid.
Each column is also a house, because it must contain digits 1 through 9.
Columns are usually numbered from 1 to 9 from left to right.
In solving techniques which affect either rows or columns, the term line is used to represent a house that can either be a row or a column.