This project tries to enhance search experience within this wiki and from other tools. The related terms are processed by tools similar to Taginfo in order to extract an up-to-date thesaurus and an API.
IMPORTANT NOTE: We are using these days a synonym editor with upload functionality. It downloads/uploads Wiki pages just like JOSM is uploading data (i.e. this is NOT a Bot!).
A related term is an association relationship between terms. In OSM it is interpreted as a general term because this makes it simpler to explain. This definition of 'related term' includes all kinds of term relationships, like synonym, broader or narrower term. See thesaurus in Wikipedia for some background.
Initial usage examples are e.g. Tag:amenity=place_of_worship.
Usage hint: Related terms are included in the list even if one could think that it's in the title, in the wiki text in order to make the set complete and explicit. The term can optionally also included when there exists a redirect page.
Related terms for programmers
The idea of related terms (synonym list, thesaurus) is that they not only enhance search in the wiki but would become a search functionality in common editors and tools. For this a webservice/API would be required. See http://tagfinder.herokuapp.com/apidoc.