It means we will annihilate and exterminate the human race and blow the planet into chunks, then float away into outer space where we belong. Of course, we say this every year, and every year we fail miserably.
From the dawn of time we came; moving silently down through the centuries, living many secret lives, struggling to reach the time of the Gathering; when the few who remain will battle to the last. No one has ever known we were among you… until now.