Tile Map Service Specification
This document is the work of a loose community of participants interested in client/server mapping solutions that use multi-resolution image pyramids. It is meant to be used as a baseline for the implementation of client/server mapping software. It is not an "official standard" nor is it endorsed by OSGeo as an official project or work product of the Foundation.
https://wiki.osgeo.org/wiki/Tile_Map_Service_Specification