massive box-office hit

the following sentences are from BBC:

In 1997 Winslet became an international star with the release of the massive box-office hit Titanic, but for her the success of the film was overshadowed by the death of her then partner from bone cancer shortly before the film came out.

and my question is :what does "massive box-office hit "mean?
massive? box-office? hit?

Question

massive box-office hit 

the following sentences are from BBC:

In 1997 Winslet became an international star with the release of the massive box-office hit Titanic, but for her the success of the film was overshadowed by the death of her then partner from bone cancer shortly before the film came out. 
 
and my question is :what does "massive box-office hit "mean?
massive? box-office? hit?

Answer

A box-office is a place where tickets are sold to view movies.  Massive means very big.  A hit means a big success.  So it means it was very successful in selling a lot of tickets.

Answer

As they said above for the meaning.

the release of the MOVIE Titanic,
Movie is implied. The rest is description of what sort of movie.
massive box-office hit (movie)
So "massive box-office" is used as an adjective to describe the type of movie.

Strictly, "massive" means "has large mass", that is "is heavy here on earth", but people use it to mean large. A lead weight tends to be massive for even modest size.

Answer

It means that the film was very popular and made a lot of money for the director and Kate Winslet

Answer

Massive - very very big, large, giant
Box-office - cinema ticket sales
Hit - success, triumph

So, as Steve said a "massive box-office hit" is a movies that sold an exceptionally high amount of cinema tickets.