Idea of Hashtag Activity Grid Icon
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 made in Material Design style
developed by Google. This style is based on extremely simplified shapes, thin two-pixel lines, and is optimized for 24x24 px. Unlike other vector icon packs that have merely hundreds of icons, this icon pack contains 6,200 icons, all in the same style and quality.