The ssdeep project page describes it as a library for "...computing context triggered piecewise hashes (CTPH). Also called fuzzy hashes, CTPH can match inputs that have homologies. Such inputs have sequences of identical bytes in the same order, although bytes in between these sequences may be different in both content and length".
For an in depth paper explaining context triggered piecewise hashes please see http://dfrws.org/2006/proceedings/12-Kornblum.pdf
This extensions wraps the ssdeep fuzzy hashing API created by Jesse Kornblum.
Documentation: http://php.net/ssdeep
Package built for PHP 8.3 as Software Collection (php83 by remi).