Mutable Data Structure is something which gives you a provision to add edit data in it. so the opposite of data structure is an Object.
Object doesn’t gives you a provision to edit its state (only in extreme conditions you do that, when no options left). Object gives behavior.
Frameworks like JEE frameworks, spring, Hibernate and others gives a false definition of POJO (mixing it with JavaBeans). i.e. a class having private fields and getter setter methods. Basically these are Data structures and not Objects.