It looks like a square or rectangular plug with the prongs facing down. There are three prongs visible with a side, rectangular profile of the center one and a thin view of the outer two.
This is a Relay 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 13,300 icons, all in the same style and quality.