Traits are a fundamental concept in programming that allows for code reuse by defining a set of methods that can be mixed into classes. They are a way to share methods among different classes without using inheritance. In essence, traits are like interfaces with implemented methods. In languages like Scala and PHP, traits enable a developer to compose classes from reusable code units. For instance, if multiple classes need to share similar behavior, instead of duplicating code across classes or using inheritance (which might lead to hierarchical constraints), you can create a trait to encapsulate that behavior and then mix it into each class that requires it. This promotes more modular and flexible code. Here's an example in PHP: trait Log { public function log($message) { echo "[" . date('Y-m-d H:i:s') . "] " . $message; } } class User { use Log; public function createUser() { $this->log('User created.'); // Other logic for creating a user } } $user = new User(); $user->createUser(); // Output: [2022-01-01 14:30:00] User created. In this example, the `Log` trait defines a `log` method that adds a timestamp to a message. By using the `use` keyword within the `User` class, the `Log` trait's methods can be accessed within the `User` class. Traits enhance code organization, promote code reuse, and prevent some of the limitations associated with traditional inheritance. They are a powerful tool in modern programming paradigms.