Gantt charts are used to show scheduling information. They are commonly used in project management but can also be used to show holiday schedule information. In this case it would be easy to see when someone is unavailable. Gantt charts can have clickable bars that can be used to provide extra detail. They can also show vertical bars that can be used to indicate events, or as in the cases below, can be decorative.
The charts are 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.