Bump keys are specially cut keys used in a lock-picking technique which involves a repeated striking motion that dislodges the pins within a lock. Research has shown the effectiveness of a bump key is about 95% when applied appropriately on locks that are susceptible to a bump key attack. The key is often used by hackers, and social engineers to gain entry when lock picks are either impractical or unavailable.
(Obvious disclaimer: In spite of their ease of use, lock bumping should only be applied during emergency/survival situations such as when you’ve accidentally locked yourself out of your home. It should not be used for illegal activities such as trespassing.)