This is a Small Icons 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 12,700 icons, all in the same style and quality.
The small icons are represented by many tiny different images or icon. For example, there may be symbols for clouds, suns, mountains, flowers, etc. The images inside the icon are small and is surrounded by a square.