It kind of looks like a little book. It's a rectangle with dashes on the side that represent the spirals of a notebook. There's a cross right on the front. Like the red cross. Or a Templar shield.
This is a Health Book 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.