how much column a cell spans in table.
Example:
<!DOCTYPE html>
<html>
<head>
<style>
table, th, td {
border: 1px solid black;
}
</style>
</head>
<body>
<h1>The td colspan attribute</h1>
<table>
<tr>
<th>Month</th>
<th>Savings</th>
</tr>
<tr>
<td>January</td>
<td>$100</td>
</tr>
<tr>
<td>February</td>
<td>$80</td>
</tr>
<tr>
<td colspan="2">Sum: $180</td>
</tr>
</table>
</body>
</html>