A Bloom filter is a space-efficient probabilistic data structure that can be used to inform the user whether a particular item is part of a set.
Understanding the Term
Developed in 1970 by Burton Howard Bloom, Bloom filters can only show with complete certainty that an item is not in the set. Though it cannot say with certainty whether an element is in the set and can present false positives at times.
Bloom filters are used to speed up answers in a key-value storage system.
Content distribution networks use them to avoid caching one-hit wonders, files that are seen only once. Web browsers use them to check for potentially harmful URLs.