This is a Ubuntu icon. We've made it in iOS style, first introduced in iOS version 7 and supported in all later releases up until now (at least iOS 11). This style is based on thin two-pixel lines and is optimized for 50x50 px. Unlike other vector icon packs that have merely hundreds of icons, this icon pack contains 12,900 icons, all in the same style and quality.
The icon is comprised of a symbol basically identical to that used by the Ubuntu Linux distribution, enclosed within a circle. Ubuntu is one of the most popular Linux distributions, favoring a Mac OS X-like graphical interface, and with widespread support for most tasks one would imagine possible with a desktop computer.