Elizabeth Ricks describes a type of visual:
Unlike other charts that use line length, position on an axis, or area to represent values, unit charts are made up of individual markers—geometric shapes, icons, images, etc—that encode quantities based on how many of that unit are shown. Examples of unit charts are ISOTYPE charts, square area charts (also known as waffle charts), symbol charts, and pictorial charts. They are commonly used in media, advertisements, and infographics.
Click through for some good use cases for unit charts.