This is a Thumbnails 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 logo is of a series of nine small squares in a grid pattern. The grid is three squares wide by three squares tall. The squares are not touching at all, there is an even amount of space between each square.