This Bookmark 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 4,400 icons, all in the same style and quality.
It's two pages of a book almost, if you were to take a piece of paper in the very middle and make an indentation as if it's curving inwards. Make those pieces inseparable, and then open it up to make a book thing. The purpose of the icon is to place a mark on a page, hence the name bookmark. It's a play on words mostly.