This is a Gniazdo pamięci 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 12,100 icons, all in the same style and quality.
This icon represents a memory slot. It is a long rectangle with four smaller rectangles inside it. On the right hand side is a slimmer, smaller rectangle that has a notch cut out in the middle and has eight lines.