Idea of External Link Icon
The icon is of an external link, made up of an arrow pointing out of the upper right corner of an unfinished box. This symbolizes linking to a resource not found within the present document.
This External Link icon is made in Material Design style
developed by Google. This style is based on extremely simplified shapes, thin two-pixel lines, and is optimized for 24x24 px. Unlike other vector icon packs that have merely hundreds of icons, this icon pack contains 6,200 icons, all in the same style and quality.