column

A column is one vertical line of a matrix — the numbers stacked top to bottom in a single standing strip, like one column of figures in an accounting ledger. Where a row goes across, a column goes down.

Columns are numbered from left to right: the first column is the leftmost strip, the second column is next to its right, and so on. A matrix with n columns has n of these vertical strips standing side by side.

The row count and the column count together give the matrix its size. They also play different structural roles — for example, in matrix multiplication the columns of one matrix must match the rows of the other in number, so keeping the two straight is essential.