what is the difference between namespace and prefix laravel code example

Example 1: laravel route namespace and prefix

Route::name('admin.')->group(function () {
    Route::get('/users', function () {
        // Route assigned name "admin.users"...
    })->name('users');
});

Example 2: laravel route namespace and prefix

Route::get('/user/{name?}', function ($name = null) {
    return $name;
});

Route::get('/user/{name?}', function ($name = 'John') {
    return $name;
});