This is a Swipe Down 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 12,300 icons, all in the same style and quality.
The "swipe down" symbol here consists of a circle, with a straight line extending down from its lower half in the middle, with two diagonal, upward-reaching lines extending upwards from the end of the line. It is a circle with a downward-pointing arrow extending from it.