Sphider is a outdated light search-engine package for adding your own search-function to a website. It has not been updated since 2007.
It's a pure PHP search-engine which stores the search-data in a MySQL database. It's a typical LAMP application which runs on any *nix server. It's not designed to be a "near-global" search-engine like YaCy or Google, it's made for a few sites.
The amount of time this software has collected dust means that you will have a hard time getting it to work with modern PHP versions.