What are the icons on the top bar called? [duplicate]
It's an "Application indicator":
Application indicators provide a simple and effective API to provide an application icon in the notification area in the top-right part of the screen, and provide simple, accessible, and complete access to key parts of your application. With bindings for C, Python, and Mono, you can integrate your app into the Unity desktop quickly and easily.
Source: https://unity.ubuntu.com/projects/appindicators/