What is the significance of adding `OR die("Error: <br>".mysql_error())` after the `mysql_query()` function in PHP?

Adding `OR die("Error: <br>".mysql_error())` after the `mysql_query()` function in PHP is significant because it helps to handle errors that may occur during the execution of the SQL query. If an error occurs, the script will stop executing and display the error message, making it easier to identify and fix the issue.

$query = mysql_query("SELECT * FROM table_name") or die("Error: <br>".mysql_error());