Asking about HTML5 date input format

I know this is a silly question but I don't really understand the format of HTML5 date input. I'm using Laravel 5.1, when I used the date input from HTML5, it had a MM/DD/YYYY format. However when I checked the value after it submited, it changed into YYYY-MM-DD. I don't really understand how it changed its format automatically like that. Please make me clear at this point. I would very appreciate. Thanks!

via Chebli Mohamed