What is an object's lock and which object's have locks? (CoreJava)

Question :What is an object's lock and which object's have locks? (CoreJava)
Answer :An object's lock is a mechanism that is used by multiple threads to obtain
synchronized access to the object. A thread may execute a synchronized
method of an object only after it has acquired the object's lock. All objects
and classes have locks. A class's lock is acquired on the class's Class
object.