It means it’s an ephemeral view. An ephemeral view is lost quicker than a normal view tab. If you open a new tab when you already have an ephemeral view open, then the ephemeral view gets replaced. This is useful if you want to quickly scan through a bunch of different files in your project. You can click on them one at a time in the file browser, and they appear in one tab, each replacing the previous file, so your tab bar doesn’t get cluttered up with a bunch of files that you only wanted to glance at. if you actually make an edit, the ephemeral view gets converted to a normal view, and the tab will stick around until you explicitly close it. You can also convert the view by double clicking on the tab.