This is a Toggle On 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 12,600 icons, all in the same style and quality.
This icon looks like a switch which can be toggled by sliding left to right. The border of the switch is a rounded oval, and the button itself is a circle which slides between two positions from left to right. The icon shows the circle in the right position.