what is the difference between these two arrays in laravel?

I am new to laravel and sometimes when I follow tutorials I see different forms of assigning the arrays' keys, can anyone explain the difference between them.

first way

$post [
'title' => 'First title',
'body'  => 'First body'
];

Second way

$post [
'title', 'First title',
'body', 'First body'
];

via Chebli Mohamed