You're right, A hash function doesn't map to multiple values. Bloom filters and other probabilistic set membership DS's like Cuckoo filters instead use multiple hash functions to map one input to multiple output values. [1] The number of hash functions to use depends on the expected false positive probability rate, number of bits in the filter and the number of elements which will be inserted

[1] : https://en.wikipedia.org/wiki/Bloom_filter#Algorithm_descrip...