This Countdown Clock 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 the image of a clock face with the number "12" written in the center. Around the clock face are the dots where the numbers of a clock would go. The circle that encloses the clock face is actually a circular arrow drawn around the clock. The arrow is pointing counter clockwise to indicate time going backwards twelve hours.