What does the title "The Fault in Our Stars" signify?

It is from a line from the play Julius Caesar, by Shakespeare:

Cassius:
The fault, dear Brutus, is not in our stars,
But in ourselves, that we are underlings.

Julius Caesar (I, ii, 140-141)

To quote from the eNotes interpretation of the play:

...Cassius continues by reminding Brutus that Caesar is just a man, not a god, and that they are equal men to Caesar. They were all born equally free, and so why would they suddenly have to bow to another man? On another level this phrase has been interpreted to mean that fate is not what drives men to their decisions and actions, but rather the human condition.

In other words, we're to blame for the badness in our lives. We have driven it, through our own actions.

However, the film is based on a book by John Green, who appears to be arguing something different.

Rather than the fault being in ourselves, that the bad stuff is because of us and our choices in life, Green's title suggests the fault is in our stars - that the bad things happen through no fault of our own. That we have little control over our own eventual fate.

The whole novel (and movie) follows this logic and shows the characters leading their lives to the fullest, despite the fault in their stars.

It means not everything or everyone is perfect . But what highlights or shines like a star in anyone or anything is those little imperfections . And we or anything are the result of those imperfections which came through situations rather than what we could have avoided.