This icon collection is released as free, open source, and GPL friendly by the Pictogrammers icon group. You may use it for commercial projects, open source projects, or anything really.
Icons: Apache 2.0 (https://www.apache.org/licenses/LICENSE-2.0)
Some of the icons are redistributed under the Apache 2.0 license. All other icons are either redistributed under their respective licenses or are distributed under the Apache 2.0 license.
Code: MIT (https://opensource.org/licenses/MIT)
The MIT license applies to all non-font and non-icon files.