A Gantt chart is used to show scheduling information. It is commonly used in project management but can also be used, for example, to show holiday schedule information. In this case it would be easy to see when someone is unavailable. The Gantt chart can have clickable bars that can be used to provide more detail. It can also show vertical bars that can be used to indicate events, or as in the case on the right, can be decorative.
The chart is made of "units", in this case 365. This represents days in a year. The labels are separate, being equally spaced across the chart. This means you can use more meaningful labels, which are easier to comprehend. As in the example charts.