What is a bloom filter index and when should I use it?

A bloom filter is a concept used to improve the performance of read operations done on specific types of computer files. More specifically, it improves the read performance of filtered read operations which only require a subset of the dataset to be returned based on specific conditions. Bloom filters improve the performance of the reading mechanism by providing "hints" which state that data is definitely not in the file, or that it is probably in the file. This allows the reading mechanism to skip certain files when reading, improving performance.