In Laravel models, what is const DATE_FORMAT = 'l jS \\of M \\@ Y g:i a';???

class Post extends BaseModel 
{   
    const DATE_FORMAT = 'l jS \\of M \\@ Y g:i a';
    public static $rules = array(
        'title' => 'required | max:255',
        'content' => 'required'

        );

use Carbon\Carbon;

class BaseModel extends Eloquent
{
    //All accessors start with the word get and use camelCase
    //these are also getters
    public function getCreatedAtAttribute($value)
    {
        //this is going into the carbon framework and creting an instance
        $utc = Carbon::createFromFormat($this->getDateFormat(), $value);

        return $utc->setTimezone('America/Chicago');
    }

    public function getUpdatedAtAttribute($value)
    {

        $utc = Carbon::createFromFormat($this->getDateFormat(), $value);

        return $utc->setTimezone('America/Chicago');
    }