This is a repackaging/reorganization of Google's Material Symbols icons, which are published at Google/material-design-icons. Specifically, these are the .svg files found within this folder.
The icons there are organized in a folder structure of 3,150 folders grouping all 504 variations of each individual glyph. Here, instead, I have grouped all 3,150 unique glyphs into 504 folders by variant. This allows you to grab a full set of icons in a chosen style variant much more easily.
This was done primarily for usage with Iconize, a plugin for Obsidian, but the full library was sorted so that it may serve some use in other applications in the future.
If you would like to explore the available glyphs in Material Symbols, check out this page on Google Fonts.