What is the meaning of "Singleton is per process and per class loader"?

"Just Spring" book says:

"Note that there is a subtle difference between the instance obtained using the Java Singleton pattern and Spring Singleton. Spring Singleton is a singleton per context or container, whereas the Java Singleton is per process and per class loader."

I do understand what "Spring Singleton is a singleton per context or container" means, but i don't understand what "Java Singleton is per process and per class loader" means. Could you please explain the last qoute?