The KDE Community
Breeze Icons
A freedesktop:org compatible icon theme.
About Breeze Icons
It's developed by the KDE Community as part of KDE Frameworks 5 and it's used by default in KDE Plasma 5 and KDE Applications.
Breeze Icons Guidelines
The Breeze icons guidelines are described in the HIG section of the KDE Community Wiki.
Breeze Icons Issues
To report actual bugs and requests for new icons fill a bug in KDE Bugtracker.