This is a Puzzle Filled 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 12,400 icons, all in the same style and quality.
This is a corner puzzle piece -one that would go in the southeast corner of a puzzle. The shape is roughly square. There is a protruding nub on the top. On the left is a space where the protrusion from another piece would fit.