Google for that term (maybe plus "java") and you'll get plenty of information.
Note that Marker Interfaces, while still used by plenty of current Java APIs, should not be created(*) in new code. If you were thinking of creating a new Marker Interface, it would usually be better to create a new type of Annotation.
(*) Note that I say "created", not "used".
Betty Rubble? Well, I would go with Betty... but I'd be thinking of Wilma.
My understanding about the Marker Interfaces is that
it is just a Flag. which is tested by the compiler to do certain things
For certain things the compiler checks weather this flag is on or not in java terms weather the Marker Interface is implemented by the class or not
for example whenever we want to serialize an Object we have to implement the Serializable interface . now when compiler sees the Markar tag( implemtts Serializable ) in a class it makes an understanding that yes this class is a candidate for serialization
There are many marker interfaces in java You just check with them