What is the significance of the "Notice: Undefined offset" error in PHP and how can it be resolved when working with arrays?

The "Notice: Undefined offset" error in PHP occurs when trying to access an index in an array that doesn't exist. This can be resolved by checking if the index exists before trying to access it using isset() or array_key_exists() functions.

// Check if the index exists before accessing it
if(isset($array[$index])) {
    // Access the index
    $value = $array[$index];
    // Perform desired operations with $value
} else {
    // Handle the case where the index is undefined
    echo "Index is undefined";
}