Singleton is an OOP concept which is used to support instantiating class only once. So basically it just uses already created instance of the class which is stored in a static variable.
Traits are one of the ways of inheritance in PHP for more detail check Traits.
This is how you can create a Trait and use it in a class.
Some points to keep in a note. In Trait, the constructor is protected so one can’t create an instance of the class by just
PHP Fatal error: Uncaught Error: Call to protected SingletonClass::__construct() from invalid context