WMS (Web Map Service) and WMTS (Web Map Tile Service) are both methods for requesting  raster data over the internet. Both are OGC standards leveraged  by a wide variety of software platforms which seek to enrich their users’ experiences with additional raster context.
A WMTS service responds to requests for imagery with many small pre-computed tile images to the software or application which is making the requests. Because of the tiled nature of the imagery backing up this service type,  users of a WMTS can be delivered  multiple images at the same time very efficiently.
Giza supports WMS as well.  A WMS service responds with a single image that has been computed on the fly from source imagery to meet the requested specification.   We recommend users leverage the WMTS service option when possible for improved imagery delivery performance.