This is a Stopwatch Filled icon. We've made it in iOS style, first introduced in iOS version 7 and supported in all later releases up until now (at least iOS 11). This style is based on thin two-pixel lines and is optimized for 50x50 px. Unlike other vector icon packs that have merely hundreds of icons, this icon pack contains 12,800 icons, all in the same style and quality.
A stopwatch is something that ticks and is handheld. It is circular with a little timer in the right so that you can click it and start + stop time. It has hands that keep track of how many seconds it has been.