Assign the key a value (apparently named $billdate) in the outer foreach loop.

foreach( $array as $billdate => $date) { 
    foreach( $date as v) {         
        echo $billdate; // Prints something like Nov 18, 2011
    }            
} 

You can use a recursive function here, so you don't need to worry how deep your array will be.

Something like this:

function read($arr) {
    foreach ($arr as $key => $value) {
        if (is_array($value)) {
            read($a);
        }
        else {
            // You cann access key and value here (for each array)
        }
    }
}

read($myArray);

Alternatively, you could use SPL RecursiveArrayIterator to get the values. Consider this example:

$values = array( 'student' => array( 'admission_no' => array('isEmpty' => 'Please enter Admission No'), 'admission_date' => array('isEmpty' => 'Please enter Admission Date'), ), 'student_personal_details' => array( 'first_name' => array('isEmpty' => 'Please enter First Name'), 'gender' => array('isEmpty' => 'Please enter Gender'), 'birth_date' => array('isEmpty' => 'Please enter Birth Date'), ), 'student_gardian_details' => array( 'first_name' => array('isEmpty' => 'Please enter Gardian First Name'), ), 'student_education_details' => array( 'roll_no' => array('isEmpty' => 'Please enter Pin Code'), ),);

$iterator = new RecursiveIteratorIterator(new RecursiveArrayIterator($values));
foreach($iterator as $key => $value) {
    $data[] = $value;
}

Sample Output:

Array
(
    [0] => Please enter Admission No
    [1] => Please enter Admission Date
    [2] => Please enter First Name
    [3] => Please enter Gender
    [4] => Please enter Birth Date
    [5] => Please enter Gardian First Name
    [6] => Please enter Pin Code
)

In php foreach() you can get key of current item like this

foreach ($array as $key=>$item){...}

Also use it like bottom code

foreach ($marks as $name=>$scores){
    echo $name .":". $scores["chemistry"];
}

See result of code in demo

Since the array elements are arrays, use array indexing to access that part of the elements:

foreach ($selected as $key => $value) {
    $binding_clause[':selected_'.$key] = $value['screenshot_id'];
}

$last = count($arr_nav) - 1;

foreach ($arr_nav as $i => $row)
{
    $isFirst = ($i == 0);
    $isLast = ($i == $last);

    echo ... $row['name'] ... $row['url'] ...;
}

You're failing to understand what foreach is doing and how arrays are structured. It iterates over each element of the given array. You've said your data looks like this:

$uploadData = [
    'filenames' => ["2.jpeg", "3.jpeg"],
    'sizes' => ["0.00 MB", "0.00 MB"],
    'temp_names' => ["/private/var/folders/np/sln14hvn3tsbzc4kpjjtp17c0000gn/T/phpLVhmBY", "/private/var/folders/np/sln14hvn3tsbzc4kpjjtp17c0000gn/T/phpoifsg0"],
    'uploads' => ["/Users/sandro/Documents/bildgalerie/uploads/2.jpeg", "/Users/sandro/Documents/bildgalerie/uploads/3.jpeg"],
];

So, this is an array with 4 elements. Each iteration of the loop will give you a new element. First iteration you get an array ["2.jpeg", "3.jpeg"] and you're trying to access the filenames element of that array. Obviously there isn't one.

Instead you can just loop over one of the sub-arrays:

foreach ($uploadData["filenames"] as $key => $value) {
    if (move_uploaded_file($uploadData["temp_names"][$key], $location . '/' . basename($value))) {
        echo 'File uploaded.';
        echo '<br>';
    }
}

On the first iteration, $key will be 0 and $value will be 2.jpeg. You can use that key to get the matching values in the other sub-arrays.

Just a quick browse of the documentation on foreach would answer this question.

The first foreach is looping through all the elements of the $people array. Each key of the array is the $name, and the value (the second-level array) is the $person.

Then in the second loop, foreach person's attribute, the type of attribute is the $key and the value of that attribute is the $value.

Please do read that manual link I just gave, it explains it far better than me!