It's a logo on many small rectangles in a grid pattern. It should be four by four but in the lower left of the image the last rectangles of the lower two rows and half of the third rectangles of the lower two rows are covered by blank space and a hashtag image.
This Hashtag Activity Grid icon is a responsive icon. This means that it's optimized for four resolutions, from tiny 16x16 until highly detailed 80x80. The style comes from the latest Microsoft Office
, which makes it perfect for any Windows applications, in particular, those with ribbon toolbar control. Unlike other icon packs that have merely hundreds of icons, this monster icon pack contains 15,900 icons, all in the same style and quality.