What is the significance of using quotes ('') in PHP code when defining strings?

Using quotes ('') in PHP code when defining strings is significant because it allows for the inclusion of variables and special characters within the string. When using single quotes, variables will not be evaluated and special characters will be treated as literal characters. To include variables or special characters within a string and have them evaluated, double quotes ("") should be used instead.

// Using double quotes to include variables within a string
$name = "John";
echo "Hello, $name!";