What are traits in PHP?

Traits in PHP are a mechanism for code reuse in single inheritance languages, allowing developers to declare reusable methods that can be used in multiple classes. This means that traits can provide a way to include functionality in classes that do not share a common ancestor, thus promoting code modularity and reducing duplication.

When a trait is defined, it contains methods that can be incorporated into a class using the use keyword. This allows the class to gain all the methods defined in the trait as if they were its own. By using traits, developers can share methods across different classes without the need for inheritance, making it easier to manage and scale code in complex applications.

The other options don't accurately capture the essence of traits. Traits are not special types of objects since they cannot be instantiated on their own. They are not simply structures for organizing functions, as their primary purpose is to facilitate method reuse across different classes. Lastly, while traits cannot be instantiated as standalone classes, the defining characteristic of traits is their role in declaring reusable methods rather than being non-instantiable entities.