Use the rowspan attribute to set the number of rows a table cell should span. To merge cells in HTML, use the colspan and rowspan attribute. The rowspan attribute is for number of rows a cell should span, whereas the colspan attribute is for number of columns a cell should span.
Example
<!DOCTYPE html>
<html>
<head>
<style>
table, th, td {
border: 1px solid black;
width: 100px;
height: 50px;
}
</style>
</head>
<body>
<h1>Heading</h1>
<table>
<tr>
<th colspan = "2"></th>
<th></th>
</tr>
<tr>
<td></td>
<td></td>
<td rowspan = "2"></td>
</tr>
<tr>
<td></td>
<td></td>
</tr>
</table>
</body>
</html>