It is an arrow pointed down. The arrow is black on a solid background. There is one solid vertical line. From the bottom of that line there are two smaller black lines extending diagonally up to the right and left at 45 degree angles.
This Down Arrow 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 5,700 icons, all in the same style and quality.