At the end of Titanic, the camera pans across a group of pictures that showed Rose had lived a rich, full life (some of which was suggested to her by Jack - e.g. learning how to ride 'like a man'). It then settles on a very peaceful looking Rose in her bed.
Then the scene segues to drop down into the inky depths of the ocean to traverse one of the upper decks of the wreck, then that transforms back to the original ship as it had looked in its splendor, turns a corner into an area of people (all of whom, I'm guessing, died during the night it sank), and up a staircase to where Jack is waiting for her in front of a clock. She takes his hand, and they embrace.
Was that to signify that she was dreaming of Jack and all those that had been lost, or had she died and joined them?