If you intend to see Christopher Nolan’s film Inception some day, then you probably will not want to continue through to rest of this post, in which I intend to succinctly spoil the ending.
You have been warned.
There are a couple of different interpretations to the ending, though if we’re to reconcile the plot holes, many would argue that only one interpretation really makes sense.
In the very final scene after the protagonist, Cobb, has successfully implanted a thought in the mind of his target and disembarks the plane to be with his children once again, he spins a top (his personal totem) meant to tell him whether or not he’s still dreaming. Just before the film cuts to black, the top wobbles. If it falls, he’s awake. If it continues spinning, he’s still dreaming.
We’re meant to be unsure, but given the fact that his children haven’t aged a day and he sees them exactly as he had been dreaming them for Nolan-only-knows how long, combined with a number of logical holes throughout the film, it makes the most sense that Cobb is stuck in his dream, and that either the entire film has been a dream–a way of finding redemption for his wife–or merely that he slipped into a sort of limbo during his escapade to perform an inception in the film’s major action.
I’ll refrain from editorializing here. You can find my review of Inception for that.