Iconify is project delivers more than 150 000 icons for further use.
Since there are lot of icons best way to look them is official iconify browser: https://icon-sets.iconify.design.
This addon is a third party extension which packs some of icons and make them available for later use by all openHAB user interfaces.
For complete readme and examples please check addon README.adoc.
Update to OH 4.0