The rows and columns in a table are described through their relationship to each other:
A column's width in one row can stretch over several columns in another row (colspan).
A row's height in one column can include more than one row in another column (rowspan).
In the description given in the html code all these relationships need to be known in advance, so that the rows/columns will be described through them from the start.

A column in Row 1 might occupy the width of two or more columns described in Row 2.
The first column's span (the number of columns in Row 2 it equals) will be indicated through the term colspan in the column's TD tag. :