This is a Open 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 12,300 icons, all in the same style and quality.
The open folder icon for pc. Manila folder that's slightly open, where files are stored. The tab is at the top left in this variant. This is what people double click to get to their information on computers.