why collection API is called as framework

I faced this interesting question in an interview.
We have several packages in java like lang, io etc, but why util package is called as framework (collection framework)?

That's really a question of definition of words, not really a technical Java knowledge question.

One reason I would think of is that the collections interfaces and classes are meant to be extended: they were designed in such a way that you can create your own special collection classes by implementing and extending the interfaces and classes of the Java collections API - in contrast to classes in other packages, which are just meant to be used (and not extended via inheritance).

@Jesper: I agree with you however I hardly ever extend the collection classes. Mainly because almost everything data-structure you would commonly need is already built.

A framework is a reusable collection of classes and interfaces so pure theoretically it's correct to call it a framework.

That's true Wouter, usually you would just use the standard ArrayList or HashMap, for example, but I guess it's about the principle - the interfaces and classes in the collections API are designed to be extensible, while many of the other standard Java classes are not designed to be extended (in fact, many of them are final, so that you can't extend them).