The Jaccard index is a statistical measure used to compare the similarity and diversity of sample sets. It is defined as the size of the intersection divided by the size of the union of two sets. This index ranges from 0 to 1, where 0 indicates no similarity and 1 indicates complete similarity. This index is commonly used in various fields, including ecology, genetics, and information retrieval, to assess the similarity between different groups or datasets. For example, in bioinformatics, the Jaccard index can help compare genetic sequences to determine how closely related different species are.