This icon looks to be an unfinished square. Instead of having the top sides connect, there is a gap that has two arrows with curved tails going into it. The arrows are pointing down.
This is a Feed In 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.