Idea of Lecture Icon
It is a picture of podium. Only the top half is drawn with a small microphone. In the bottom half, instead of the podium, there are small circles indicating there is an audience. There are seven circles in total.
This Lecture 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.