Material Design Icons are open source icons. These are officially open-source icons featured by Google.

Material Design Icons Included?

i. SVG versions of all icons in both 24px and 48px flavours
ii. SVG and CSS sprites of all icons
iii. 1×1, 2×2 for Web (PNG)
iv. 1×1, 2×2, 3×3 for iOS (PNG)
v. Hi-dpi (dot per inch) versions of all icons (hdpi, mdpi, xhdpi, xxhdpi, xxxhdpi) (PNG)

Google Material Design Icons
Google Material Design Icons

Material Icons Type:

1. action
2. Alert
3. communication
4. av
5. content
6. device
7. editor
8. file
9. hardware
10. image
11. maps
12. navigation
13. notification
14. social
15. toggle

Links:

http://google.github.io/material-design-icons/ (preview of icons set)
Download Zip archive
Licence
github link
Material Design icons (spec) by Google