This is the name of a design pattern that establishes a Class that will only have one object instance.

In code, you can go like this:

this.ServiceProvider().GetEcoService<IExtentService>().AllInstances(typeof(YourClass))[0].GetValue<YourClass>()

In ocl/eal, go like this:

YourClass.oclSingleton or YourClass.allinstances->first