A relation would be BCNF when functional dependencies are like $x->y$ ; where x is super key and in that way when attributes are dependent on super key , redundancy can't exist.
But what will happen when we have such a relation that doesn't contain any non-trivial functional dependency?Hope you can guess that in such case super key will be the whole set of attributes.So eventually we can say such a relation will be BCNF relation. Can we say that this kind of relation will be free of redundancies ? There comes the term call 'Multivalued dependency', whose presence make the relation redundant. like
You can see , this relation is in BCNF as no functional dependencies exist there.
But here exists multivalued dependencies (basically multivalued dependency means multiple values of some attributes are dependent on some attribute value )