Gantt Bar is represented with the icon.

A Gantt Bar uses a Continuous field (generally a Date) in Rows or Columns to set the initial position and another Continuous field in Size. The Gantt Bar is generally used to create a Gantt chart. This visualization is helpful when you manage projects over time or if you want to create a timeline, as in the following screenshot:

I built this Gantt chart for my resume. As you can see, there is a Continuous Date in columns and the number of days in Size. With this visualization, you can see when the different events started and their length.

The next Mark type is very uncommon, and you'll need a particular dataset to use it: Polygon.