A Java singleton, per the design pattern where instantiation is restricted to one, usually per JVM class loader by the code. Wikipedia
A Spring singleton bean can be any normal class you write, but declaring it's scope as singleton means that Spring will only create one instance and provide its reference to all beans that reference the declared bean. You may have many instances of that class in your application, but only one will be created for that bean. You may even have multiple beans of the same class all declared as singleton. Each bean will create exactly one instance of the class. Spring 3.1 Doc
