Blackout/ˈblækaʊt/ Definition 1 of 5Pro Tip 1/2Unexpected Event Blackouts are often unplanned. People use this term when the electricity goes off suddenly. We were watching a movie when a blackout occurred. Pro Tip 2/2Temporary Problem A blackout usually lasts for a short time and is not permanent. The blackout lasted just long enough to ruin our dinner plans.