Four main types of probabilistic data structures are described: membership, cardinality, frequency, and similarity. Bloom filters and cuckoo filters are discussed as membership data structures that can tell if an element is definitely not or may be in a set. Cardinality structures like HyperLogLog are able to estimate large cardinalities with small error rates. Count-Min Sketch is presented as a frequency data structure. MinHash and locality sensitive hashing are covered as similarity data structures that can efficiently find similar documents in large datasets.