We sometimes need singletons in our programming. A singleton is a single static global instance of some object, where that instance is the only possible instance of its class.

A top-level val property is close to a singleton, in that it is a static global instance of some object. However, other code could create an instance of the class via the class' constructor. So, here, QUASI_SINGLETON is not truly a singleton.

• the documentation
• Elements of Kotlin