It's a logo of a piece of paper with the upper right side of the paper folded over slightly to make a triangle. Inside the paper are the letters "J2K" written slightly below center.
This is a J2K 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 13,100 icons, all in the same style and quality.