How can undefined array key errors be avoided in PHP?

Undefined array key errors in PHP can be avoided by checking if the key exists before trying to access it. This can be done using the `isset()` function to determine if the key is set in the array. By checking if the key exists before accessing it, you can prevent PHP from throwing an error when trying to access an undefined key.

// Check if the key exists before accessing it
if(isset($array['key'])) {
    // Access the key if it exists
    $value = $array['key'];
    // Use the value here
} else {
    // Handle the case where the key is undefined
    echo "Key does not exist in the array";
}