MUMmer is a bioinformatics software system for sequence alignment. It is based on the suffix tree data structure and is one of the fastest and most efficient systems available for this task, enabling it to be applied to very long sequences. It has been widely used for comparing different genomes to one another. In recent years it has become a popular algorithm for comparing genome assemblies to one another, which allows scientists to determine how a genome has changed after adding more DNA sequence or after running a different genome assembly program. The acronym "MUMmer" comes from "Maximal Unique Matches", or MUMs. The original algorithms in the MUMMER software package were designed by Art Delcher, Simon Kasif and Steven Salzberg. Mummer was the first whole genome comparison system developed in Bioinformatics. It was originally applied to comparison of two related strains of bacteria.

Mummers Plays are seasonal British folk plays, performed by troupes of amateur actors known as mummers or guisers (or by local names such as rhymers, pace-eggers, soulers, tipteerers, wrenboys, galoshins, guysers, and so on). Originally from the British Isles, the practice has spread to a number of former British colonies. They are sometimes performed in the street, but more usually as house-to-house visits and in local pubs.