Table cells can span multiple columns or rows using the colspan and rowspan attributes. These attributes can be applied to <th> and <td> elements.

<table>
    <tr>
        <td>row 1 col 1</td>
        <td>row 1 col 2</td>
        <td>row 1 col 3</td>
    </tr>
    <tr>
        <td colspan="3">This second row spans all three columns</td>
    </tr>
    <tr>
        <td rowspan="2">This cell spans two rows</td>
        <td>row 3 col 2</td>
        <td>row 3 col 3</td>
    </tr>
    <tr>
        <td>row 4 col 2</td>
        <td>row 4 col 3</td>
    </tr>

</table>

Will result in

Note that you should not design a table where both rows and columns overlap as this is invalid HTML and the result is handled differently by different web browsers.

rowspan = A non-negative integer that specifies the number of rows spanned by a cell. The default value of this attribute is one (1). A value of zero (0) means that the cell will extend from the current row until the last row of the table (<thead>, <tbody>, or <tfoot>).

colspan = A non-negative integer that specifies the number of columns spanned by the current cell. The default value of this attribute is one (1). A value of zero (0) means that the cell will extend from the current to the last column of the column group <colgroup> in which the cell is defined.