What is the difference between "=" and "" in the scope options of a custom policy?

In AngularJS, I was creating a directive.

I noticed that when I used the = sign to capture a certain value from the controller scope, when I changed this value, the value of the parent controller was also changing.

For example:

angular.module('app', [])

.controller('Parent', function ($scope) {

    $scope.users = [{name: "Jonh"}, {name: "Wallace"}];

    $scope.user = $scope.nomes[0];
})

.directive('userMoreInfo', function () {

    var directive = {
        replace: true,
        restrict: 'E',
        template: '<button ng-click="showInfo(user)">info</button>',
        scope: {
            os: '='
        }
    }; 

    directive.controller = function ($scope) {

        $scope.showInfo = function (user, modal) {

            $http.get('/mais-informacoes/' + user.id).then(function (response) {

                // isso aqui tá alterando o valor do controller pai

                $scope.user = response.data; 

                // restante do código (não relevante à pergunta)
            })
        };
    };
})

Call:

 <div ng-controller="Parent">
      <ul>
          <li ng-repeat="user in users">
             {{ user.name }}
             <user-more-info></user-more-info>
          </li>
      </ul>
 </div>

But I did not want that to happen. I wanted to use the scope property with the same name, without affecting the parent controller.

I ended up using < and it worked as I wanted.

On the surface, I understood that% with a% value so that "two sides" are affected. And = assigns the value so that it gets isolated in < of the directive.

So, I would like to know in detail what are the main differences between these two operators, regarding the form of assignment of scope of a certain directive.